HTML 5.1

6.1.1 Nested browsing contexts

Certain elements (for example, iframe elements) can instantiate further browsing contexts. These are called nested browsing contexts. If a browsing context P has a Document D with an element E that nests another browsing context C inside it, then C is said to be nested through D, and E is said to be the browsing context container of C. If the browsing context container element E is in the Document D, then P is said to be the parent browsing context of C and C is said to be a child browsing context of P. Otherwise, the nested browsing context C has no parent browsing context.

A browsing context A is said to be an ancestor of a browsing context B if there exists a browsing context A' that is a child browsing context of A and that is itself an ancestor of B, or if the browsing context A is the parent browsing context of B.

A browsing context that is not a nested browsing context has no parent browsing context, and is the top-level browsing context of all the browsing contexts for which it is an ancestor browsing context.

The transitive closure of parent browsing contexts for a nested browsing context gives the list of ancestor browsing contexts.

The list of the descendant browsing contexts of a Document d is the (ordered) list returned by the following algorithm:

1. Let list be an empty list.

2. For each child browsing context of d that is nested through an element that is in the Document d, in the tree order of the elements nesting those browsing contexts, run these substeps:

   1. Append that child browsing context to the list list.

   2. Append the list of the descendant browsing contexts of the active document of that child browsing context to the list list.

3. Return the constructed list.

A Document is said to be fully active when it is the active document of its browsing context, and either its browsing context is a top-level browsing context, or it has a parent browsing context and the Document through which it is nested is itself fully active.

Because they are nested through an element, child browsing contexts are always tied to a specific Document in their parent browsing context. User agents must not allow the user to interact with child browsing contexts of elements that are in Documents that are not themselves fully active.

A nested browsing context can have a seamless browsing context flag set, if it is embedded through an iframe element with a seamless attribute.

A nested browsing context can be put into a delaying load events mode. This is used when it is navigated, to delay the load event of the browsing context container before the new Document is created.

The document family of a browsing context consists of the union of all the Document objects in that browsing context's session history and the document families of all those Document objects. The document family of a Document object consists of the union of all the document families of the browsing contexts that are nested through the Document object.

6.1.2 Auxiliary browsing contexts

It is possible to create new browsing contexts that are related to a top-level browsing context without being nested through an element. Such browsing contexts are called auxiliary browsing contexts. Auxiliary browsing contexts are always top-level browsing contexts.

An auxiliary browsing context has an opener browsing context, which is the browsing context from which the auxiliary browsing context was created.

6.1.3 Secondary browsing contexts

User agents may support secondary browsing contexts, which are browsing contexts that form part of the user agent's interface, apart from the main content area.

6.1.4 Security

A browsing context A is familiar with a second browsing context B if one of the following conditions is true:

• Either the origin of the active document of A is the same as the origin of the active document of B, or
• The browsing context A is a nested browsing context with a top-level browsing context, and its top-level browsing context is B, or
• The browsing context B is an auxiliary browsing context and A is familiar with B's opener browsing context, or
• The browsing context B is not a top-level browsing context, but there exists an ancestor browsing context of B whose active document has the same origin as the active document of A (possibly in fact being A itself).

A browsing context A is allowed to navigate a second browsing context B if the following algorithm terminates positively:

1. If A is not the same browsing context as B, and A is not one of the ancestor browsing contexts of B, and B is not a top-level browsing context, and A's active document's active sandboxing flag set has its sandboxed navigation browsing context flag set, then abort these steps negatively.

2. Otherwise, if B is a top-level browsing context, and is one of the ancestor browsing contexts of A, and A's node document's active sandboxing flag set has its sandboxed top-level navigation browsing context flag set, then abort these steps negatively.

3. Otherwise, if B is a top-level browsing context, and is neither A nor one of the ancestor browsing contexts of A, and A's Document's active sandboxing flag set has its sandboxed navigation browsing context flag set, and A is not the one permitted sandboxed navigator of B, then abort these steps negatively.

4. Otherwise, terminate positively!

An element has a browsing context scope origin if its Document's browsing context is a top-level browsing context or if all of its Document's ancestor browsing contexts all have active documents whose origin are the same origin as the element's node document's origin. If an element has a browsing context scope origin, then its value is the origin of the element's node document.

6.1.5 Groupings of browsing contexts

Each browsing context is defined as having a list of one or more directly reachable browsing contexts. These are:

• The browsing context itself.
• All the browsing context's child browsing contexts.
• The browsing context's parent browsing context.
• All the browsing contexts that have the browsing context as their opener browsing context.
• The browsing context's opener browsing context.

The transitive closure of all the browsing contexts that are directly reachable browsing contexts forms a unit of related browsing contexts.

Each unit of related browsing contexts is then further divided into the smallest number of groups such that every member of each group has an active document with an effective script origin that, through appropriate manipulation of the document.domain attribute, could be made to be the same as other members of the group, but could not be made the same as members of any other group. Each such group is a unit of related similar-origin browsing contexts.

There is also at most one event loop per unit of related similar-origin browsing contexts (though several units of related similar-origin browsing contexts can have a shared event loop).

6.1.6 Browsing context names

Browsing contexts can have a browsing context name. By default, a browsing context has no name (its name is not set).

A valid browsing context name is any string with at least one character that does not start with a U+005F LOW LINE character. (Names starting with an underscore are reserved for special keywords.)

A valid browsing context name or keyword is any string that is either a valid browsing context name or that is an ASCII case-insensitive match for one of: _blank, _self, _parent, or _top.

These values have different meanings based on whether the page is sandboxed or not, as summarised in the following (non-normative) table. In this table, "current" means the browsing context that the link or script is in, "parent" means the parent browsing context of the one the link or script is in, "master" means the nearest ancestor browsing context of the one the link or script is in that is not itself in a seamless iframe, "top" means the top-level browsing context of the one the link or script is in, "new" means a new top-level browsing context or auxiliary browsing context is to be created, subject to various user preferences and user agent policies, "none" means that nothing will happen, and "maybe new" means the same as "new" if the "allow-popups" keyword is also specified on the sandbox attribute (or if the user overrode the sandboxing), and the same as "none" otherwise.

Most of the restrictions on sandboxed browsing contexts are applied by other algorithms, e.g. the navigation algorithm, not the rules for choosing a browsing context given a browsing context name given below.

An algorithm is allowed to show a popup if any of the following conditions is true:

• The task in which the algorithm is running is currently processing an activation behaviour whose click event was trusted.

• The task in which the algorithm is running is currently running the event listener for a trusted event whose type is in the following list:

  • change
  • click
  • dblclick
  • mouseup
  • reset
  • submit

• The task in which the algorithm is running was queued by an algorithm that was allowed to show a popup, and the chain of such algorithms started within a user-agent defined timeframe.

  For example, if a user clicked a button, it might be acceptable for a popup to result from that after 4 seconds, but it would likely not be acceptable for a popup to result from that after 4 hours.

The rules for choosing a browsing context given a browsing context name are as follows. The rules assume that they are being applied in the context of a browsing context, as part of the execution of a task.

1. If the given browsing context name is the empty string or _self, then the chosen browsing context must be the current one.

   If the given browsing context name is _self, then this is an explicit self-navigation override, which overrides the behaviour of the seamless browsing context flag set by the seamless attribute on iframe elements.

2. If the given browsing context name is _parent, then the chosen browsing context must be the parent browsing context of the current one, unless there isn't one, in which case the chosen browsing context must be the current browsing context.

3. If the given browsing context name is _top, then the chosen browsing context must be the top-level browsing context of the current one, if there is one, or else the current browsing context.

4. If the given browsing context name is not _blank and there exists a browsing context whose name is the same as the given browsing context name, and the current browsing context is familiar with that browsing context, and the user agent determines that the two browsing contexts are related enough that it is ok if they reach each other, then that browsing context must be the chosen one. If there are multiple matching browsing contexts, the user agent should select one in some arbitrary consistent manner, such as the most recently opened, most recently focused, or more closely related.

   If the browsing context is chosen by this step to be the current browsing context, then this is also an explicit self-navigation override.

5. Otherwise, a new browsing context is being requested, and what happens depends on the user agent's configuration and abilities — it is determined by the rules given for the first applicable option from the following list:

   If the algorithm is not allowed to show a popup and the user agent has been configured to not show popups (i.e. the user agent has a "popup blocker" enabled)

   There is no chosen browsing context. The user agent may inform the user that a popup has been blocked.

   If the current browsing context's active document's active sandboxing flag set has the sandboxed auxiliary navigation browsing context flag set.

   Typically, there is no chosen browsing context.

   The user agent may offer to create a new top-level browsing context or reuse an existing top-level browsing context. If the user picks one of those options, then the designated browsing context must be the chosen one (the browsing context's name isn't set to the given browsing context name). The default behaviour (if the user agent doesn't offer the option to the user, or if the user declines to allow a browsing context to be used) must be that there must not be a chosen browsing context.

   If this case occurs, it means that an author has explicitly sandboxed the document that is trying to open a link.

   If the user agent has been configured such that in this instance it will create a new browsing context, and the browsing context is being requested as part of following a hyperlink whose link types include the noreferrer keyword

   A new top-level browsing context must be created. If the given browsing context name is not _blank, then the new top-level browsing context's name must be the given browsing context name (otherwise, it has no name). The chosen browsing context must be this new browsing context. The creation of such a browsing context is a new start for session storage.

   If it is immediately navigated, then the navigation will be done with replacement enabled.

   If the user agent has been configured such that in this instance it will create a new browsing context, and the noreferrer keyword doesn't apply

   A new auxiliary browsing context must be created, with the opener browsing context being the current one. If the given browsing context name is not _blank, then the new auxiliary browsing context's name must be the given browsing context name (otherwise, it has no name). The chosen browsing context must be this new browsing context.

   If it is immediately navigated, then the navigation will be done with replacement enabled.

   If the user agent has been configured such that in this instance it will reuse the current browsing context

   The chosen browsing context is the current browsing context.

   If the user agent has been configured such that in this instance it will not find a browsing context

   There must not be a chosen browsing context.

   User agent implementors are encouraged to provide a way for users to configure the user agent to always reuse the current browsing context.

   If the current browsing context's active document's active sandboxing flag set has both the sandboxed navigation browsing context flag and sandbox propagates to auxiliary browsing contexts flag set, and the chosen browsing context picked above, if any, is a new browsing context, then all the flags that are set in the current browsing context's active document's active sandboxing flag set when the new browsing context is created must be set in the new browsing context's popup sandboxing flag set, and the current browsing context must be set as the new browsing context's one permitted sandboxed navigator.

6.2.1 Security

This section describes a security model that is underdefined, imperfect, and does not match implementations. Work is ongoing to attempt to resolve this, but in the meantime, please do not rely on this section for precision. Implementors are urged to send their feedback on how cross-origin cross-global access to Window and Location objects should work. See bug 20701.

User agents must throw a SecurityError exception whenever any properties of a Window object are accessed when the incumbent settings object specifies an effective script origin that is not the same as the Window object's Document's effective script origin, with the following exceptions:

• The location attribute
• The postMessage() method
• The window attribute
• The frames attribute
• The self attribute
• The top attribute
• The parent attribute
• The opener attribute
• The closed attribute
• The close() method
• The blur() method
• The focus() method
• The dynamic nested browsing context properties

When the incumbent settings object specifies an effective script origin that is different than a Window object's Document's effective script origin, the user agent must act as if any changes to that Window object's properties, getters, setters, etc, were not present, and as if all the properties of that Window object had their [[Enumerable]] attribute set to false.

For members that return objects (including function objects), each distinct effective script origin that is not the same as the Window object's Document's effective script origin must be provided with a separate set of objects. These objects must have the prototype chain appropriate for the script for which the objects are created (not those that would be appropriate for scripts whose global object, as specified by their settings object, is the Window object in question).

6.2.2 APIs for creating and navigating browsing contexts by name

window = window . open( [ url [, target [, features [, replace ] ] ] ] )

Opens a window to show url (defaults to about:blank), and returns it. The target argument gives the name of the new window. If a window exists with that name already, it is reused. The replace attribute, if true, means that whatever page is currently open in that window will be removed from the window's session history. The features argument can be used to influence the rendering of the new window.

window . name [ = value ]

Returns the name of the window.

Can be set, to change the name.

window . close()

Closes the window.

window . closed

Returns true if the window has been closed, false otherwise.

window . stop()

Cancels the document load.

The open() method on Window objects provides a mechanism for navigating an existing browsing context or opening and navigating an auxiliary browsing context.

When the method is invoked, the user agent must run the following steps:

1. Let entry settings be the entry settings object when the method was invoked.

2. Let url be the first argument.

3. Let target be the second argument.

4. Let features be the third argument.

5. Let replace be the fourth argument.

6. Let source browsing context be the responsible browsing context specified by entry settings.

7. If target is the empty string, let it be the string "_blank" instead.

8. If the user has indicated a preference for which browsing context to navigate, follow these substeps:

   1. Let target browsing context be the browsing context indicated by the user.

   2. If target browsing context is a new top-level browsing context, let the source browsing context be set as target browsing context's one permitted sandboxed navigator.

   For example, suppose there is a user agent that supports control-clicking a link to open it in a new tab. If a user clicks in that user agent on an element whose onclick handler uses the window.open() API to open a page in an iframe, but, while doing so, holds the control key down, the user agent could override the selection of the target browsing context to instead target a new tab.

   Otherwise, apply the rules for choosing a browsing context given a browsing context name using target as the name and source browsing context as the context in which the algorithm is executed. If this results in there not being a chosen browsing context, then throw an InvalidAccessError exception and abort these steps. Otherwise, let target browsing context be the browsing context so obtained.

9. If target browsing context was just created, either as part of the rules for choosing a browsing context given a browsing context name or due to the user indicating a preference for navigating a new top-level browsing context, then let new be true. Otherwise, let it be false.

10. Interpret features as defined in the CSSOM View specification. [CSSOMVIEW]

11. If url is the empty string, run the appropriate steps from the following list:

    If new is false

    Jump to the step labeled end.

    If new is true

    Let resource be the URL "about:blank".

    Otherwise, resolve url relative to the API base URL specified by entry settings, and let resource be the resulting absolute URL, if any. If the resolve a URL algorithm failed, then run one of the following two steps instead:

    • Let resource be a resource representing an inline error page.

    • If new is false, jump to the step labeled end, otherwise, let resource be the URL "about:blank".

12. If resource is "about:blank" and new is true, queue a task to fire a simple event named load at target browsing context's Window object, with target override set to target browsing context's Window object's Document object.

    Otherwise, navigate target browsing context to resource, with exceptions enabled. If new is true, then replacement must be enabled also. The source browsing context is source browsing context.

13. End: Return the WindowProxy object of target browsing context.

The name attribute of the Window object must, on getting, return the current name of the browsing context, if one is set, or the empty string otherwise; and, on setting, set the name of the browsing context to the new value.

The name gets reset when the browsing context is navigated to another domain.

The close() method on Window objects should, if all the following conditions are met, close the browsing context A:

• The corresponding browsing context A is script-closable.
• The responsible browsing context specified by the incumbent settings object is familiar with the browsing context A.
• The responsible browsing context specified by the incumbent settings object is allowed to navigate the browsing context A.

A browsing context is script-closable if it is an auxiliary browsing context that was created by a script (as opposed to by an action of the user), or if it is a top-level browsing context whose session history contains only one Document.

The closed attribute on Window objects must return true if the Window object's browsing context has been discarded, and false otherwise.

The stop() method on Window objects should, if there is an existing attempt to navigate the browsing context and that attempt is not currently running the unload a document algorithm, cancel that navigation; then, it must abort the active document of the browsing context of the Window object on which it was invoked.

6.2.3 Accessing other browsing contexts

window . length

Returns the number of child browsing contexts.

window[index]

Returns the indicated child browsing context.

The length IDL attribute on the Window interface must return the number of child browsing contexts that are nested through elements that are in the Document that is the active document of that Window object, if that Window's browsing context shares the same event loop as the responsible document specified by the entry settings object accessing the IDL attribute; otherwise, it must return zero.

The supported property indices on the Window object at any instant are the numbers in the range 0 .. n-1, where n is the number returned by the length IDL attribute. If n is zero then there are no supported property indices.

To determine the value of an indexed property index of a Window object, the user agent must return the WindowProxy object of the indexth child browsing context of the Document that is nested through an element that is in the Document, sorted in the order that the elements nesting those browsing contexts were most recently inserted into the Document, the WindowProxy object of the most recently inserted browsing context container's nested browsing context being last.

These properties are the dynamic nested browsing context properties.

6.2.4 Named access on the Window object

window[name]

Returns the indicated element or collection of elements.

As a general rule, relying on this will lead to brittle code. Which IDs end up mapping to this API can vary over time, as new features are added to the Web platform, for example. Instead of this, use document.getElementById() or document.querySelector().

The Window interface supports named properties. The supported property names at any moment consist of the following, in tree order, ignoring later duplicates:

• the browsing context name of any child browsing context of the active document whose name is not the empty string,
• the value of the name content attribute for all a, applet, area, embed, form, frameset, img, and object elements in the active document that have a non-empty name content attribute, and
• the value of the id content attribute of any HTML element in the active document with a non-empty id content attribute.

The properties exposed in this way must be unenumerable.

To determine the value of a named property name when the Window object is indexed for property retrieval, the user agent must return the value obtained using the following steps:

1. Let objects be the list of named objects with the name name in the active document.

   There will be at least one such object, by definition.

2. If objects contains a nested browsing context, then return the WindowProxy object of the nested browsing context corresponding to the first browsing context container in tree order whose browsing context is in objects, and abort these steps.

3. Otherwise, if objects has only one element, return that element and abort these steps.

4. Otherwise return an HTMLCollection rooted at the Document node, whose filter matches only named objects with the name name. (By definition, these will all be elements.)

Named objects with the name name, for the purposes of the above algorithm, are those that are either:

• child browsing contexts of the active document whose name is name,
• a, applet, area, embed, form, frameset, img, or object elements that have a name content attribute whose value is name, or
• HTML elements that have an id content attribute whose value is name.

6.2.5 Garbage collection and browsing contexts

A browsing context has a strong reference to each of its Documents and its WindowProxy object, and the user agent itself has a strong reference to its top-level browsing contexts.

A Document has a strong reference to its Window object.

A Window object has a strong reference to its Document object through its document attribute. Thus, references from other scripts to either of those objects will keep both alive. Similarly, both Document and Window objects have implied strong references to the WindowProxy object.

Each script has a strong reference to its settings object, and each environment settings object has strong references to its global object, responsible browsing context, and responsible document (if any).

When a browsing context is to discard a Document, the user agent must run the following steps:

1. Set the Document's salvageable state to false.

2. Run any unloading document cleanup steps for the Document that are defined by this specification and other applicable specifications.

3. Abort the Document.

4. Remove any tasks associated with the Document in any task source, without running those tasks.

5. Discard all the child browsing contexts of the Document.

6. Lose the strong reference from the Document's browsing context to the Document.

Whenever a Document object is discarded, it is also removed from the list of the worker's Documents of each worker whose list contains that Document.

When a browsing context is discarded, the strong reference from the user agent itself to the browsing context must be severed, and all the Document objects for all the entries in the browsing context's session history must be discarded as well.

User agents may discard top-level browsing contexts at any time (typically, in response to user requests, e.g. when a user force-closes a window containing one or more top-level browsing contexts). Other browsing contexts must be discarded once their WindowProxy object is eligible for garbage collection.

6.2.6 Closing browsing contexts

When the user agent is required to close a browsing context, it must run the following steps:

1. Let specified browsing context be the browsing context being closed.

2. Prompt to unload the active document of the specified browsing context. If the user refused to allow the document to be unloaded, then abort these steps.

3. Unload the active document of the specified browsing context with the recycle parameter set to false.

4. Remove the specified browsing context from the user interface (e.g. close or hide its tab in a tabbed browser).

5. Discard the specified browsing context.

User agents should offer users the ability to arbitrarily close any top-level browsing context.

6.2.7 Browser interface elements

To allow Web pages to integrate with Web browsers, certain Web browser interface elements are exposed in a limited way to scripts in Web pages.

Each interface element is represented by a BarProp object:

interface BarProp {
  readonly attribute boolean visible;
};

window . locationbar . visible

Returns true if the location bar is visible; otherwise, returns false.

window . menubar . visible

Returns true if the menu bar is visible; otherwise, returns false.

window . personalbar . visible

Returns true if the personal bar is visible; otherwise, returns false.

window . scrollbars . visible

Returns true if the scroll bars are visible; otherwise, returns false.

window . statusbar . visible

Returns true if the status bar is visible; otherwise, returns false.

window . toolbar . visible

Returns true if the toolbar is visible; otherwise, returns false.

The visible attribute, on getting, must return either true or a value determined by the user agent to most accurately represent the visibility state of the user interface element that the object represents, as described below.

The following BarProp objects exist for each Document object in a browsing context. Some of the user interface elements represented by these objects might have no equivalent in some user agents; for those user agents, except when otherwise specified, the object must act as if it was present and visible (i.e. its visible attribute must return true).

The location bar BarProp object

Represents the user interface element that contains a control that displays the URL of the active document, or some similar interface concept.

The menu bar BarProp object

Represents the user interface element that contains a list of commands in menu form, or some similar interface concept.

The personal bar BarProp object

Represents the user interface element that contains links to the user's favorite pages, or some similar interface concept.

The scrollbar BarProp object

Represents the user interface element that contains a scrolling mechanism, or some similar interface concept.

The status bar BarProp object

Represents a user interface element found immediately below or after the document, as appropriate for the user's media, which typically provides information about ongoing network activity or information about elements that the user's pointing device is current indicating. If the user agent has no such user interface element, then the object may act as if the corresponding user interface element was absent (i.e. its visible attribute may return false).

The toolbar BarProp object

Represents the user interface element found immediately above or before the document, as appropriate for the user's media, which typically provides session history traversal controls (back and forward buttons, reload buttons, etc). If the user agent has no such user interface element, then the object may act as if the corresponding user interface element was absent (i.e. its visible attribute may return false).

The locationbar attribute must return the location bar BarProp object.

The menubar attribute must return the menu bar BarProp object.

The personalbar attribute must return the personal bar BarProp object.

The scrollbars attribute must return the scrollbar BarProp object.

The statusbar attribute must return the status bar BarProp object.

The toolbar attribute must return the toolbar BarProp object.

For historical reasons, the status attribute on the Window object must, on getting, return the last string it was set to, and on setting, must set itself to the new value. When the Window object is created, the attribute must be set to the empty string. It does not do anything else.

6.2.8 The WindowProxy object

As mentioned earlier, each browsing context has a WindowProxy object. This object is unusual in that all operations that would be performed on it must be performed on the Window object of the browsing context's active document instead. It is thus indistinguishable from that Window object in every way until the browsing context is navigated.

There is no WindowProxy interface object.

The WindowProxy object allows scripts to act as if each browsing context had a single Window object, while still keeping separate Window objects for each Document.

var x = window;
x instanceof Window; // true
x === this; // true

6.3.1 Relaxing the same-origin restriction

document . domain [ = domain ]

Returns the current domain used for security checks.

Can be set to a value that removes subdomains, to change the effective script origin to allow pages on other subdomains of the same domain (if they do the same thing) to access each other. (Can't be set in sandboxed iframes.)

The domain attribute on Document objects must be initialised to the document's domain, if it has one, and the empty string otherwise. If the document's domain starts with a U+005B LEFT SQUARE BRACKET character ([) and ends with a U+005D RIGHT SQUARE BRACKET character (]), it is an IPv6 address; these square brackets must be omitted when initialising the attribute's value.

On getting, the attribute must return its current value, unless the Document has no browsing context, in which case it must return the empty string.

On setting, the user agent must run the following algorithm:

1. If the Document has no browsing context, throw a SecurityError exception and abort these steps.

2. If the Document's active sandboxing flag set has its sandboxed document.domain browsing context flag set, throw a SecurityError exception and abort these steps.

3. If the new value is an IPv4 or IPv6 address, let new value be the new value.

   Otherwise, strictly split the new value on U+002E FULL STOP characters (.), apply the domain to ASCII algorithm to each returned token, and let new value be the result of concatenating the results of applying that algorithm to each token, in the same order, separated by U+002E FULL STOP characters (.). [URL]

   If the domain to ASCII algorithm returns failure, e.g. because a component is too long or because it contains invalid characters, then throw a SecurityError exception and abort these steps.

4. If new value is not exactly equal to the current value of the document.domain attribute, then run these substeps:

   1. If the current value is an IPv4 or IPv6 address, throw a SecurityError exception and abort these steps.

   2. If new value, prefixed by a U+002E FULL STOP (.), does not exactly match the end of the current value, throw a SecurityError exception and abort these steps.

      If the new value is an IPv4 or IPv6 address, it cannot match the new value in this way and thus an exception will be thrown here.

   3. If new value matches a suffix in the Public Suffix List, or, if new value, prefixed by a U+002E FULL STOP (.), matches the end of a suffix in the Public Suffix List, then throw a SecurityError exception and abort these steps. [PSL]

      Suffixes must be compared in an ASCII case-insensitive manner, after applying the domain to ASCII algorithm to their individual components, . [URL]

5. Release the storage mutex.

6. Set the attribute's value to new value.

7. If the effective script origin of the Document is an alias, set it to the value of the effective script origin (essentially de-aliasing the effective script origin).

8. If new value is not the empty string, then run these substeps:

   1. Set the host part of the effective script origin tuple of the Document to new value.

   2. Set the port part of the effective script origin tuple of the Document to "manual override" (a value that, for the purposes of comparing origins, is identical to "manual override" but not identical to any other value).

The domain of a Document is the host part of the document's origin, if the value of that origin is a scheme/host/port tuple. If it isn't, then the document does not have a domain.

The domain attribute is used to enable pages on different hosts of a domain to access each others' DOMs.

Do not use the document.domain attribute when using shared hosting. If an untrusted third party is able to host an HTTP server at the same IP address but on a different port, then the same-origin protection that normally protects two different sites on the same host will fail, as the ports are ignored when comparing origins after the document.domain attribute has been used.

6.5.1 The session history of browsing contexts

The sequence of Documents in a browsing context is its session history. Each browsing context, including nested browsing contexts, has a distinct session history. A browsing context's session history consists of a flat list of session history entries. Each session history entry consists, at a minimum, of a URL, and each entry may in addition have a state object, a title, a Document object, form data, a scroll position, and other information associated with it.

Each entry, when first created, has a Document. However, when a Document is not active, it's possible for it to be discarded to free resources. The URL and other data in a session history entry is then used to bring a new Document into being to take the place of the original, should the user agent find itself having to reactivate that Document.

Titles associated with session history entries need not have any relation with the current title of the Document. The title of a session history entry is intended to explain the state of the document at that point, so that the user can navigate the document's history.

URLs without associated state objects are added to the session history as the user (or script) navigates from page to page.

Each Document object in a browsing context's session history is associated with a unique History object which must all model the same underlying session history.

The history attribute of the Window interface must return the object implementing the History interface for that Window object's newest Document.

A state object is an object representing a user interface state.

Pages can add state objects to the session history. These are then returned to the script when the user (or script) goes back in the history, thus enabling authors to use the "navigation" metaphor even in one-page applications.

At any point, one of the entries in the session history is the current entry. This is the entry representing the active document of the browsing context. Which entry is the current entry is changed by the algorithms defined in this specification, e.g. during session history traversal.

The current entry is usually an entry for the address of the Document. However, it can also be one of the entries for state objects added to the history by that document.

An entry with persisted user state is one that also has user-agent defined state. This specification does not specify what kind of state can be stored.

For example, some user agents might want to persist the scroll position, or the values of form controls.

User agents that persist the value of form controls are encouraged to also persist their directionality (the value of the element's dir attribute). This prevents values from being displayed incorrectly after a history traversal when the user had originally entered the values with an explicit, non-default directionality.

Entries that consist of state objects share the same Document as the entry for the page that was active when they were added.

Contiguous entries that differ just by fragment identifier also share the same Document.

All entries that share the same Document (and that are therefore merely different states of one particular document) are contiguous by definition.

Each Document in a browsing context can also have a latest entry. This is the entry for that Document to which the browsing context's session history was most recently traversed. When a Document is created, it initially has no latest entry.

User agents may discard the Document objects of entries other than the current entry that are not referenced from any script, reloading the pages afresh when the user or script navigates back to such pages. This specification does not specify when user agents should discard Document objects and when they should cache them.

Entries that have had their Document objects discarded must, for the purposes of the algorithms given below, act as if they had not. When the user or script navigates back or forwards to a page which has no in-memory DOM objects, any other entries that shared the same Document object with it must share the new object as well.

6.5.2 The History interface

interface History {
  readonly attribute unsigned long length;
  readonly attribute any state;
  void go(optional long delta = 0);
  void back();
  void forward();
  void pushState(any data, DOMString title, optional DOMString? url = null);
  void replaceState(any data, DOMString title, optional DOMString? url = null);
};

window . history . length

Returns the number of entries in the joint session history.

window . history . state

Returns the current state object.

window . history . go( [ delta ] )

Goes back or forward the specified number of steps in the joint session history.

A zero delta will reload the current page.

If the delta is out of range, does nothing.

window . history . back()

Goes back one step in the joint session history.

If there is no previous page, does nothing.

window . history . forward()

Goes forward one step in the joint session history.

If there is no next page, does nothing.

window . history . pushState(data, title [, url ] )

Pushes the given data onto the session history, with the given title, and, if provided and not null, the given URL.

window . history . replaceState(data, title [, url ] )

Updates the current entry in the session history to have the given data, title, and, if provided and not null, URL.

The joint session history of a top-level browsing context is the union of all the session histories of all browsing contexts of all the fully active Document objects that share that top-level browsing context, with all the entries that are current entries in their respective session histories removed except for the current entry of the joint session history.

The current entry of the joint session history is the entry that most recently became a current entry in its session history.

Entries in the joint session history are ordered chronologically by the time they were added to their respective session histories. Each entry has an index; the earliest entry has index 0, and the subsequent entries are numbered with consecutively increasing integers (1, 2, 3, etc).

Since each Document in a browsing context might have a different event loop, the actual state of the joint session history can be somewhat nebulous. For example, two sibling iframe elements could both traverse from one unique origin to another at the same time, so their precise order might not be well-defined; similarly, since they might only find out about each other later, they might disagree about the length of the joint session history.

All the getters and setters for attributes, and all the methods, defined on the History interface, when invoked on a History object associated with a Document that is not fully active, must throw a SecurityError exception instead of operating as described below.

The length attribute of the History interface must return the number of entries in the top-level browsing context's joint session history.

The actual entries are not accessible from script.

The state attribute of the History interface must return the last value it was set to by the user agent. Initially, its value must be null.

When the go(delta) method is invoked, if delta is zero, the user agent must act as if the location.reload() method was called instead. Otherwise, the user agent must traverse the history by a delta whose value is delta.

When the back() method is invoked, the user agent must traverse the history by a delta −1.

When the forward()method is invoked, the user agent must traverse the history by a delta +1.

Each top-level browsing context has a session history traversal queue, initially empty, to which tasks can be added.

Each top-level browsing context, when created, must begin running the following algorithm, known as the session history event loop for that top-level browsing context, in parallel:

1. Wait until this top-level browsing context's session history traversal queue is not empty.

2. Pull the first task from this top-level browsing context's session history traversal queue, and execute it.

3. Return to the first step of this algorithm.

The session history event loop helps coordinate cross-browsing-context transitions of the joint session history: since each browsing context might, at any particular time, have a different event loop (this can happen if the user agent has more than one event loop per unit of related browsing contexts), transitions would otherwise have to involve cross-event-loop synchronisation.

To traverse the history by a delta delta, the user agent must append a task to this top-level browsing context's session history traversal queue, the task consisting of running the following steps:

1. Let delta be the argument to the method.

2. If the index of the current entry of the joint session history plus delta is less than zero or greater than or equal to the number of items in the joint session history, then abort these steps.

3. Let specified entry be the entry in the joint session history whose index is the sum of delta and the index of the current entry of the joint session history.

4. Let specified browsing context be the browsing context of the specified entry.

5. If the specified browsing context's active document's unload a document algorithm is currently running, abort these steps.

6. Queue a task that consists of running the following substeps. The relevant event loop is that of the specified browsing context's active document. The task source for the queued task is the history traversal task source.

   1. If there is an ongoing attempt to navigate specified browsing context that has not yet matured (i.e. it has not passed the point of making its Document the active document), then cancel that attempt to navigate the browsing context.

   2. If the specified browsing context's active document is not the same Document as the Document of the specified entry, then run these substeps:

      1. Fully exit fullscreen.

      2. Prompt to unload the active document of the specified browsing context. If the user refused to allow the document to be unloaded, then abort these steps.

      3. Unload the active document of the specified browsing context with the recycle parameter set to false.

   3. Traverse the history of the specified browsing context to the specified entry.

When the user navigates through a browsing context, e.g. using a browser's back and forward buttons, the user agent must traverse the history by a delta equivalent to the action specified by the user.

The pushState(data, title, url) method adds a state object entry to the history.

The replaceState(data, title, url) method updates the state object, title, and optionally the URL of the current entry in the history.

When either of these methods is invoked, the user agent must run the following steps:

1. Let cloned data be a structured clone of the specified data. If this throws an exception, then rethrow that exception and abort these steps.

2. If the third argument is not null, run these substeps:

   1. Resolve the value of the third argument, relative to the API base URL specified by the entry settings object.
   2. If that fails, throw a SecurityError exception and abort these steps.
   3. Compare the resulting parsed URL to the result of applying the URL parser algorithm to the document's address. If any component of these two URLs differ other than the path, query, and fragment components, then throw a SecurityError exception and abort these steps.
   4. If the origin of the resulting absolute URL is not the same as the origin of the responsible document specified by the entry settings object, and either the path or query components of the two parsed URLs compared in the previous step differ, throw a SecurityError exception and abort these steps. (This prevents sandboxed content from spoofing other pages on the same origin.)

   5. Let new URL be the resulting absolute URL.

   For the purposes of the comparisons in the above substeps, the path and query components can only be the same if the scheme component of both parsed URLs are relative schemes.

3. If the third argument is null, then let new URL be the URL of the current entry.

4. If the method invoked was the pushState() method:

   1. Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.

      This doesn't necessarily have to affect the user agent's user interface.

   2. Remove any tasks queued by the history traversal task source that are associated with any Document objects in the top-level browsing context's document family.

   3. If appropriate, update the current entry to reflect any state that the user agent wishes to persist. The entry is then said to be an entry with persisted user state.

   4. Add a state object entry to the session history, after the current entry, with cloned data as the state object, the given title as the title, and new URL as the URL of the entry.

   5. Update the current entry to be this newly added entry.

   Otherwise, if the method invoked was the replaceState() method:

   1. Update the current entry in the session history so that cloned data is the entry's new state object, the given title is the new title, and new URL is the entry's new URL.

5. If the current entry in the session history represents a non-GET request (e.g. it was the result of a POST submission) then update it to instead represent a GET request.

6. Set the document's address to new URL.

   Since this is neither a navigation of the browsing context nor a history traversal, it does not cause a hashchange event to be fired.

7. Set history.state to a structured clone of cloned data.

8. Let the latest entry of the Document of the current entry be the current entry.

The title is purely advisory. User agents might use the title in the user interface.

User agents may limit the number of state objects added to the session history per page. If a page hits the UA-defined limit, user agents must remove the entry immediately after the first entry for that Document object in the session history after having added the new entry. (Thus the state history acts as a FIFO buffer for eviction, but as a LIFO buffer for navigation.)

<!DOCTYPE HTML>
<!-- this is http://example.com/line?x=5 -->
<title>Line Game - 5</title>
<p>You are at coordinate 5 on the line.</p>
<p>
 <a href="?x=6">Advance to 6</a> or
 <a href="?x=4">retreat to 4</a>?
</p>

<!DOCTYPE HTML>
<!-- this starts off as http://example.com/line?x=5 -->
<title>Line Game - 5</title>
<p>You are at coordinate <span id="coord">5</span> on the line.</p>
<p>
 <a href="?x=6" onclick="go(1); return false;">Advance to 6</a> or
 <a href="?x=4" onclick="go(-1); return false;">retreat to 4</a>?
</p>
<script>
 var currentPage = 5; // prefilled by server
 function go(d) {
   setupPage(currentPage + d);
   history.pushState(currentPage, document.title, '?x=' + currentPage);
 }
 onpopstate = function(event) {
   setupPage(event.state);
 }
 function setupPage(page) {
   currentPage = page;
   document.title = 'Line Game - ' + currentPage;
   document.getElementById('coord').textContent = currentPage;
   document.links[0].href = '?x=' + (currentPage+1);
   document.links[0].textContent = 'Advance to ' + (currentPage+1);
   document.links[1].href = '?x=' + (currentPage-1);
   document.links[1].textContent = 'retreat to ' + (currentPage-1);
 }
</script>

<!DOCTYPE HTML>
<TITLE>Line</TITLE>
<SCRIPT>
 setInterval(function () { document.title = 'Line - ' + new Date(); }, 1000);
 var i = 1;
 function inc() {
   set(i+1);
   history.pushState(i, 'Line - ' + i);
 }
 function set(newI) {
   i = newI;
   document.forms.F.I.value = newI;
 }
</SCRIPT>
<BODY ONPOPSTATE="set(event.state)">
<FORM NAME=F>
State: <OUTPUT NAME=I>1</OUTPUT> <INPUT VALUE="Increment" TYPE=BUTTON ONCLICK="inc()">
</FORM>

6.5.3 The Location interface

Each Document object in a browsing context's session history is associated with a unique instance of a Location object.

document . location [ = value ]

window . location [ = value ]

Returns a Location object with the current page's location.

Can be set, to navigate to another page.

The location attribute of the Document interface must return the Location object for that Document object, if it is in a browsing context, and null otherwise.

The location attribute of the Window interface must return the Location object for that Window object's Document.

Location objects provide a representation of the address of the active document of their Document's browsing context, and allow the current entry of the browsing context's session history to be changed, by adding or replacing entries in the history object.

[Unforgeable] interface Location {
  stringifier attribute USVString href;
           attribute USVString origin;
           attribute USVString protocol;
           attribute USVString host;
           attribute USVString hostname;
           attribute USVString port;
           attribute USVString pathname;
           attribute USVString search;
           attribute USVString hash;

  void assign(USVString url);
  void replace(USVString url);
  void reload();

  [SameObject] readonly attribute USVString[] ancestorOrigins;
};

location . toString()

location . href

Returns the Location object's URL.

Can be set, to navigate to the given URL.

location . origin

Returns the Location object's URL's origin.

location . protocol

Returns the Location object's URL's scheme.

Can be set, to navigate to the same URL with a changed scheme.

location . host

Returns the Location object's URL's host and port (if different from the default port for the scheme).

Can be set, to navigate to the same URL with a changed host and port.

location . hostname

Returns the Location object's URL's host.

Can be set, to navigate to the same URL with a changed host.

location . port

Returns the Location object's URL's port.

Can be set, to navigate to the same URL with a changed port.

location . pathname

Returns the Location object's URL's path.

Can be set, to navigate to the same URL with a changed path.

location . search

Returns the Location object's URL's query (includes leading "?" if non-empty).

Can be set, to navigate to the same URL with a changed query (ignores leading "?").

location . hash

Returns the Location object's URL's fragment (includes leading "#" if non-empty).

Can be set, to navigate to the same URL with a changed fragment (ignores leading "#").

location . assign(url)

Navigates to the given URL.

location . replace(url)

Removes the current page from the session history and navigates to the given URL.

location . reload()

Reloads the current page.

location . ancestorOrigins

Returns an array whose values are the origins of the ancestor browsing contexts, from the parent browsing context to the top-level browsing context.

A Location object has an associated relevant Document, which is this Location object's associated Document object's browsing context's active document.

A Location object has an associated url, which is this Location object's relevant Document's address.

A Location object has an associated Location-object-setter navigate algorithm, which given a url, runs these steps:

1. If any of the following conditions are met, let replacement flag be unset; otherwise, let it be set:

   • This Location object's relevant Document has completely loaded, or
   • In the task in which the algorithm is running, an activation behaviour is currently being processed whose click event was trusted, or
   • In the task in which the algorithm is running, the event listener for a trusted click event is being handled.

2. Location-object navigate, given url and replacement flag.

To Location-object navigate, given a url and replacement flag, run these steps:

1. The source browsing context is the responsible browsing context specified by the incumbent settings object.

2. Navigate the browsing context to url, with exceptions enabled.

   If the replacement flag is set or the browsing context's session history contains only one Document, and that was the about:blank Document created when the browsing context was created, then the navigation must be done with replacement enabled.

The href attribute's getter must return this Location object's url, serialised.

The href attribute's setter must run these steps:

1. Let newURL be the resulting parsed URL of resolving the given value relative to the entry settings object's API base URL.

2. If that aborted with an error, throw a TypeError exception.

3. Location-object-setter navigate to newURL.

The origin attribute's getter must return the Unicode serialization of this Location object's url's origin.

It returns the Unicode rather than the ASCII serialisation for compatibility with MessageEvent.

The protocol attribute's getter must return this Location object's url's scheme, followed by ":".

The protocol attribute's setter must run these steps:

1. Let copyURL be a copy of this Location object's url.

2. Let possibleFailure be the result of basic URL parsing the given value, followed by ":", with copyURL as url and scheme start state as state override.

3. If possibleFailure is failure, throw a TypeError exception.

4. If copyURL's scheme is not "http" or "https", terminate these steps.

5. Location-object-setter navigate to copyURL.

The host attribute's getter must run these steps:

1. Let url be this Location object's url.

2. If url's host is null, return the empty string.

3. If url's port is null, return url's host, serialised.

4. Return url's host, serialised, followed by ":" and url's port, serialised.

The host attribute's setter must run these steps:

1. Let copyURL be a copy of this Location object's url.

2. If copyURL's non-relative flag is set, terminate these steps.

3. Basic URL parse the given value, with copyURL as url and host state as state override.

4. Location-object-setter navigate to copyURL.

The hostname attribute's getter must run these steps:

1. If this Location object's url's host is null, return the empty string.

2. Return this Location object's url's host, serialised.

The hostname attribute's setter must run these steps:

1. Let copyURL be a copy of this Location object's url.

2. If copyURL's non-relative flag is set, terminate these steps.

3. Basic URL parse the given value, with copyURL as url and hostname state as state override.

4. Location-object-setter navigate to copyURL.

The port attribute's getter must run these steps:

1. If this Location object's url's port is null, return the empty string.

2. Return this Location object's url's port, serialised.

The port attribute's setter must run these steps:

1. Let copyURL be a copy of this Location object's url.

2. If copyURL's host is null, copyURL's non-relative flag is set, or copyURL's scheme is "file", terminate these steps.

3. Basic URL parse the given value, with copyURL as url and port state as state override.

4. Location-object-setter navigate to copyURL.

The pathname attribute's getter must run these steps:

1. Let url be this Location object's url.

2. If url's non-relative flag is set, return the first string in url's path.

3. Return "/", followed by the strings in url's path (including empty strings), separated from each other by "/".

The pathname attribute's setter must run these steps:

1. Let copyURL be a copy of this Location object's url.

2. If copyURL's non-relative flag is set, terminate these steps.

3. Set copyURL's path to the empty list.

4. Basic URL parse the given value, with copyURL as url and path start state as state override.

5. Location-object-setter navigate to copyURL.

The search attribute's getter must run these steps:

1. If this Location object's url's query is either null or the empty string, return the empty string.

2. Return "?", followed by this Location object's url's query.

The search attribute's setter must run these steps:

1. Let copyURL be a copy of this Location object's url.

2. If the given value is the empty string, set copyURL's query to null.

3. Otherwise, run these substeps:

   1. Let input be the given value with a single leading "?" removed, if any.

   2. Set copyURL's query to the empty string.

   3. Basic URL parse input, with copyURL as url and query state as state override, and the relevant Document's document's character encoding as encoding override.

4. Location-object-setter navigate to copyURL.

The hash attribute's getter must run these steps:

1. If this Location object's url's fragment is either null or the empty string, return the empty string.

2. Return "#", followed by this Location object's url's fragment.

The hash attribute's setter must run these steps:

1. Let copyURL be a copy of this Location object's url.

2. If copyURL's scheme is "javascript", terminate these steps.

3. If the given value is the empty string, set copyURL's fragment to null.

4. Otherwise, run these substeps:

   1. Let input be the given value with a single leading "#" removed, if any.

   2. Set copyURL's fragment to the empty string.

   3. Basic URL parse input, with copyURL as url and fragment state as state override.

5. Location-object-setter navigate to copyURL.

When the assign(url) method is invoked, the user agent must run the following steps:

1. Resolve url, relative to the API base URL specified by the entry settings object and let parsedURL be the resulting parsed URL.

   If this is not successful, throw a SyntaxError exception and abort these steps.

2. Location-object navigate to parsedURL.

When the replace(url) method is invoked, the user agent must run the following steps:

1. Resolve url, relative to the API base URL specified by the entry settings object and let parsedURL be the resulting parsed URL.

   If this is not successful, throw a SyntaxError exception and abort these steps.

2. Location-object navigate to parsedURL with the replacement flag set.

When the reload() method is invoked, the user agent must run the appropriate steps from the following list:

If the currently executing task is the dispatch of a resize event in response to the user resizing the browsing context

Repaint the browsing context and abort these steps.

If the browsing context's active document is an iframe srcdoc document

Reprocess the iframe attributes of the browsing context's browsing context container.

If the browsing context's active document has its reload override flag set

Perform an overridden reload, with the browsing context being navigated as the responsible browsing context.

Otherwise

Navigate the browsing context to the document's address with replacement enabled and exceptions enabled. The source browsing context must be the browsing context being navigated. This is a reload-triggered navigation.

When a user requests that the active document of a browsing context be reloaded through a user interface element, the user agent should navigate the browsing context to the same resource as that Document, with replacement enabled. In the case of non-idempotent methods (e.g. HTTP POST), the user agent should prompt the user to confirm the operation first, since otherwise transactions (e.g. purchases or database modifications) could be repeated. User agents may allow the user to explicitly override any caches when reloading. If browsing context's active document's reload override flag is set, then the user agent may instead perform an overridden reload rather than the navigation described in this paragraph (with the browsing context being reloaded as the source browsing context).

The ancestorOrigins attribute, on getting, must return a read only array whose values are determined as follows. The same object must be returned each time the attribute's value is obtained for any particular Location object.

1. Let output be an empty ordered list of strings.

2. Let current be the browsing context of the Document with which the Location object is associated.

3. Loop: If current has no parent browsing context, jump to the step labeled end.

4. Let current be current's parent browsing context.

5. Append the Unicode serialisation of current's active document's origin to output as a new value.

6. Return to the step labeled loop.

7. End: Let output be the values of the array, in the same order.

6.5.4 Implementation notes for session history

This section is non-normative.

The History interface is not meant to place restrictions on how implementations represent the session history to the user.

For example, session history could be implemented in a tree-like manner, with each page having multiple "forward" pages. This specification doesn't define how the linear list of pages in the history object are derived from the actual session history as seen from the user's perspective.

Similarly, a page containing two iframes has a history object distinct from the iframes' history objects, despite the fact that typical Web browsers present the user with just one "Back" button, with a session history that interleaves the navigation of the two inner frames and the outer page.

Security: It is suggested that to avoid letting a page "hijack" the history navigation facilities of a UA by abusing pushState(), the UA provide the user with a way to jump back to the previous page (rather than just going back to the previous state). For example, the back button could have a drop down showing just the pages in the session history, and not showing any of the states. Similarly, an aural browser could have two "back" commands, one that goes back to the previous state, and one that jumps straight back to the previous page.

In addition, a user agent could ignore calls to pushState() that are invoked on a timer, or from event listeners that are not triggered in response to a clear user action, or that are invoked in rapid succession.

6.6.1 Navigating across documents

Certain actions cause the browsing context to navigate to a new resource. A user agent may provide various ways for the user to explicitly cause a browsing context to navigate, in addition to those defined in this specification.

For example, following a hyperlink, form submission, and the window.open() and location.assign() methods can all cause a browsing context to navigate.

A resource has a URL, but that might not be the only information necessary to identify it. For example, a form submission that uses HTTP POST would also have the HTTP method and payload. Similarly, an iframe srcdoc document needs to know the data it is to use.

Navigation always involves source browsing context, which is the browsing context which was responsible for starting the navigation.

When a browsing context is navigated to a new resource, the user agent must run the following steps:

1. Release the storage mutex.

2. If the source browsing context is not allowed to navigate the browsing context being navigated, then abort these steps.

   If these steps are aborted here, the user agent may instead offer to open the new resource in a new top-level browsing context or in the top-level browsing context of the source browsing context, at the user's option, in which case the user agent must navigate that designated top-level browsing context to the new resource as if the user had requested it independently.

   Doing so, however, can be dangerous, as it means that the user is overriding the author's explicit request to sandbox the content.

   If the navigate algorithm was invoked with exceptions enabled, and it is aborted on this step, then in addition to aborting this algorithm, the user agent must also throw a SecurityError exception.

3. If the source browsing context is the same as the browsing context being navigated, and this browsing context has its seamless browsing context flag set, and the browsing context being navigated was not chosen using an explicit self-navigation override, then find the nearest ancestor browsing context that does not have its seamless browsing context flag set, and continue these steps as if that browsing context was the one that was going to be navigated instead.

4. If there is a preexisting attempt to navigate the browsing context, and the source browsing context is the same as the browsing context being navigated, and that attempt is currently running the unload a document algorithm, and the origin of the URL of the resource being loaded in that navigation is not the same origin as the origin of the URL of the resource being loaded in this navigation, then abort these steps without affecting the preexisting attempt to navigate the browsing context.

5. If a task queued by the traverse the history by a delta algorithm is running the unload a document algorithm for the active document of the browsing context being navigated, then abort these steps without affecting the unload a document algorithm or the aforementioned history traversal task.

6. If the prompt to unload a document algorithm is being run for the active document of the browsing context being navigated, then abort these steps without affecting the prompt to unload a document algorithm.

7. Let gone async be false.

   The handle redirects step later in this algorithm can in certain cases jump back to the step labeled fragment identifiers. Since, between those two steps, this algorithm goes from operating synchronously in the context of the calling task to operating in parallel independent of the event loop, some of the intervening steps need to be able to handle both being run as part of a task and running in parallel. The gone async flag is thus used to make these steps aware of which mode they are operating in.

8. Fragment identifiers: If this is not a reload-triggered navigation: apply the URL parser algorithm to the absolute URL of the new resource and the address of the active document of the browsing context being navigated; if all the components of the resulting parsed URLs, ignoring any fragment components, are identical, and the new resource is to be fetched using `GET`, and the parsed URL of the new resource has a fragment component that is not null (even if it is empty), then navigate to that fragment identifier and abort these steps.

9. If gone async is false, cancel any preexisting but not yet mature attempt to navigate the browsing context, including canceling any instances of the fetch algorithm started by those attempts. If one of those attempts has already created and initialised a new Document object, abort that Document also. (Navigation attempts that have matured already have session history entries, and are therefore handled during the update the session history with the new page algorithm, later.)

10. If the new resource is to be handled using a mechanism that does not affect the browsing context, e.g. ignoring the navigation request altogether because the specified scheme is not one of the supported protocols, then abort these steps and proceed with that mechanism instead.

11. If gone async is false, prompt to unload the Document object. If the user refused to allow the document to be unloaded, then abort these steps.

    If this instance of the navigation algorithm gets canceled while this step is running, the prompt to unload a document algorithm must nonetheless be run to completion.

12. If gone async is false, abort the active document of the browsing context.

13. If the new resource is to be handled by displaying some sort of inline content, e.g. an error message because the specified scheme is not one of the supported protocols, or an inline prompt to allow the user to select a registered handler for the given scheme, then display the inline content and abort these steps.

    In the case of a registered handler being used, the algorithm will be reinvoked with a new URL to handle the request.

14. If the browsing context being navigated is a nested browsing context, then put it in the delaying load events mode.

    The user agent must take this nested browsing context out of the delaying load events mode when this navigation algorithm later matures, or when it terminates (whether due to having run all the steps, or being canceled, or being aborted), whichever happens first.

15. This is the step that attempts to obtain the resource, if necessary. Jump to the first appropriate substep:

    If the resource has already been obtained (e.g. because it is being used to populate an object element's new child browsing context)

    Skip this step. The data is already available.

    If the new resource is a URL whose scheme is javascript

    Queue a task to run these "javascript: URL" steps, associated with the active document of the browsing context being navigated:

    1. If the origin of the source browsing context is not the same origin as the origin of the active document of the browsing context being navigated, then act as if the result of evaluating the script was the void value, and jump to the step labeled process results below.

    2. Apply the URL parser to the URL being navigated.

    3. Let parsed URL be the result of the URL parser.

    4. Let script source be the empty string.

    5. Append parsed URL's scheme data component to script source.

    6. If parsed URL's query component is not null, then first append a U+003F QUESTION MARK character (?) to script source, and then append parsed URL's query component to script source.

    7. If parsed URL's fragment component is not null, then first append a U+0023 NUMBER SIGN character (#) to script source, and then append parsed URL's fragment component to script source.

    8. Replace script source with the result of applying the percent decode algorithm to script source.

    9. Replace script source with the result of applying the UTF-8 decode algorithm to script source.

    10. Let address be the address of the active document of the browsing context being navigated.

    11. Create a script, using script source as the script source, address as the script source URL, JavaScript as the scripting language, and the environment settings object of the Window object of the active document of the browsing context being navigated.

        Let result be the return value of the code entry-point of this script. If an exception was thrown, let result be void instead. (The result will be void also if scripting is disabled.)

    12. Process results: If the result of executing the script is void (there is no return value), then the result of obtaining the resource for the URL is a response whose status is 204.

        Otherwise, the result of obtaining the resource for the URL is a response whose header list consists of Content-Type/text/html and whose body is the return value converted to a string value.

        When it comes time to set the document's address in the navigation algorithm, use address as the override URL.

    The task source for this task is the DOM manipulation task source.

    So for example a javascript: URL in an href attribute of an a element would only be evaluated when the link was followed, while such a URL in the src attribute of an iframe element would be evaluated in the context of the iframe's own nested browsing context when the iframe is being set up; once evaluated, its return value (if it was not void) would replace that browsing context's Document, thus also changing the Window object of that browsing context.

    If the new resource is to be fetched using `GET`, and there are relevant application caches that are identified by a URL with the same origin as the URL in question, and that have this URL as one of their entries, excluding entries marked as foreign, and whose mode is fast, and the user agent is not in a mode where it will avoid using application caches

    Fetch the resource from the most appropriate application cache of those that match.

    For example, imagine an HTML page with an associated application cache displaying an image and a form, where the image is also used by several other application caches. If the user right-clicks on the image and chooses "View Image", then the user agent could decide to show the image from any of those caches, but it is likely that the most useful cache for the user would be the one that was used for the aforementioned HTML page. On the other hand, if the user submits the form, and the form does a POST submission, then the user agent will not use an application cache at all; the submission will be made to the network.

    This still needs to be integrated with the Fetch standard. [FETCH]

    Otherwise

    1. Let request be the new resource.

    2. If request is a URL, set request to a new request whose url is request.

    3. Set request's client to the source browsing context's active document's Window object's environment settings object, target browsing context to the browsing context being navigated, destination to "document", mode to "navigate", credentials mode to "include", use-URL-credentials flag, and redirect mode to "manual".

    4. Set request's omit-Origin-header flag.

    5. If request's method is not `GET`, or, if the navigation algorithm was invoked as a result of the form submission algorithm, then if there is an origin of the active document of the source browsing context, unset request's omit-Origin-header flag.

    6. Otherwise, if the browsing context being navigated is a child browsing context, and the browsing context container of the browsing context being navigated has a browsing context scope origin, set request's origin to that browsing context scope origin and unset request's omit-Origin-header flag.

    7. Fetch request.

16. If gone async is false, return to whatever algorithm invoked the navigation steps and continue running these steps asynchronously.

17. Let gone async be true.

18. Wait for one or more bytes to be available or for the user agent to establish that the resource in question is empty. During this time, the user agent may allow the user to cancel this navigation attempt or start other navigation attempts.

19. Handle redirects: If fetching the resource results in a redirect, and either the URL of the target of the redirect has the same origin as the original resource, or the resource is being obtained using the POST method or a safe method (in HTTP terms), return to the step labeled fragment identifiers with the new resource, except that if the URL of the target of the redirect does not have a fragment identifier and the URL of the resource that led to the redirect does, then the fragment identifier of the resource that led to the redirect must be propagated to the URL of the target of the redirect.

    So for instance, if the original URL was "http://example.com/#!sample" and "http://example.com/" is found to redirect to "https://example.com/", the URL of the new resource will be "https://example.com/#!sample".

    Otherwise, if fetching the resource results in a redirect but the URL of the target of the redirect does not have the same origin as the original resource and the resource is being obtained using a method that is neither the POST method nor a safe method (in HTTP terms), then abort these steps. The user agent may indicate to the user that the navigation has been aborted for security reasons.

20. Fallback in prefer-online mode: If the resource was not fetched from an application cache, and was to be fetched using `GET`, and there are relevant application caches that are identified by a URL with the same origin as the URL in question, and that have this URL as one of their entries, excluding entries marked as foreign, and whose mode is prefer-online, and the user didn't cancel the navigation attempt during the earlier step, and the navigation attempt failed (e.g. the server returned a 4xx or 5xx status, or there was a DNS error), then:

    Let candidate be the resource identified by the URL in question from the most appropriate application cache of those that match.

    If candidate is not marked as foreign, then the user agent must discard the failed load and instead continue along these steps using candidate as the resource. The user agent may indicate to the user that the original page load failed, and that the page used was a previously cached resource.

    This does not affect the address of the resource from which Request-URIs are obtained, as used to set the document's referrer in the initialise the Document object steps below; they still use the value as computed by the original fetch algorithm.

21. Fallback for fallback entries: If the resource was not fetched from an application cache, and was to be fetched using `GET`, and its URL matches the fallback namespace of one or more relevant application caches, and the most appropriate application cache of those that match does not have an entry in its online whitelist that has the same origin as the resource's URL and that is a prefix match for the resource's URL, and the user didn't cancel the navigation attempt during the earlier step, and the navigation attempt failed (e.g. the server returned a 4xx or 5xx status, or there was a DNS error), then:

    Let candidate be the fallback resource specified for the fallback namespace in question. If multiple application caches match, the user agent must use the fallback of the most appropriate application cache of those that match.

    If candidate is not marked as foreign, then the user agent must discard the failed load and instead continue along these steps using candidate as the resource. The document's address, if appropriate, will still be the originally requested URL, not the fallback URL, but the user agent may indicate to the user that the original page load failed, that the page used was a fallback resource, and what the URL of the fallback resource actually is.

    This does not affect the address of the resource from which Request-URIs are obtained, as used to set the document's referrer in the initialise the Document object steps below; they still use the value as computed by the original fetch algorithm.

22. Resource handling: If the resource's out-of-band metadata (e.g. HTTP headers), not counting any type information (such as the Content-Type HTTP header), requires some sort of processing that will not affect the browsing context, then perform that processing and abort these steps.

    Such processing might be triggered by, amongst other things, the following:

    • HTTP status codes (e.g. 204 No Content or 205 Reset Content)
    • Network errors (e.g. the network interface being unavailable)
    • Cryptographic protocol failures (e.g. an incorrect TLS certificate)

    Responses with HTTP `Content-Disposition` headers specifying the attachment disposition type must be handled as a download.

    HTTP 401 responses that do not include a challenge recognised by the user agent must be processed as if they had no challenge, e.g. rendering the entity body as if the response had been 200 OK.

    User agents may show the entity body of an HTTP 401 response even when the response does include a recognised challenge, with the option to login being included in a non-modal fashion, to enable the information provided by the server to be used by the user before authenticating. Similarly, user agents should allow the user to authenticate (in a non-modal fashion) against authentication challenges included in other responses such as HTTP 200 OK responses, effectively allowing resources to present HTTP login forms without requiring their use.

23. Let type be the sniffed type of the resource.

24. If the user agent has been configured to process resources of the given type using some mechanism other than rendering the content in a browsing context, then skip this step. Otherwise, if the type is one of the following types, jump to the appropriate entry in the following list, and process the resource as described there:

    an HTML MIME type

    Follow the steps given in the HTML document section, and then, once they have completed, abort this navigate algorithm.

    an XML MIME type that is not an explicitly supported XML type

    Follow the steps given in the XML document section. If that section determines that the content is not to be displayed as a generic XML document, then proceed to the next step in this overall set of steps. Otherwise, once the steps given in the XML document section have completed, abort this navigate algorithm.

    a JavaScript MIME type

    a JSON MIME type that is not an explicitly supported JSON type

    "text/cache-manifest"

    "text/css"

    "text/plain"

    "text/vtt"

    Follow the steps given in the plain text file section, and then, once they have completed, abort this navigate algorithm.

    "multipart/x-mixed-replace"

    Follow the steps given in the multipart/x-mixed-replace section, and then, once they have completed, abort this navigate algorithm.

    A supported image, video, or audio type

    Follow the steps given in the media section, and then, once they have completed, abort this navigate algorithm.

    A type that will use an external application to render the content in the browsing context

    Follow the steps given in the plugin section, and then, once they have completed, abort this navigate algorithm.

    An explicitly supported XML type is one for which the user agent is configured to use an external application to render the content (either a plugin rendering directly in the browsing context, or a separate application), or one for which the user agent has dedicated processing rules (e.g. a Web browser with a built-in Atom feed viewer would be said to explicitly support the application/atom+xml MIME type), or one for which the user agent has a dedicated handler (e.g. one registered using registerContentHandler()).

    The term JSON MIME type is used to refer to the MIME types application/json, text/json, and any MIME type whose subtype ends with the five characters "+json".

    An explicitly supported JSON type is one for which the user agent is configured to use an external application to render the content (either a plugin rendering directly in the browsing context, or a separate application), or one for which the user agent has dedicated processing rules, or one for which the user agent has a dedicated handler (e.g. one registered using registerContentHandler()).

    Setting the document's address: If there is no override URL, then any Document created by these steps must have its address set to the URL that was originally to be fetched, ignoring any other data that was used to obtain the resource. However, if there is an override URL, then any Document created by these steps must have its address set to that URL instead.

    An override URL is set when dereferencing a javascript: URL and when performing an overridden reload.

    Initialising a new Document object: when a Document is created as part of the above steps, the user agent will be required to additionally run the following algorithm after creating the new object:

    1. Create a new Window object, and associate it with the Document, with one exception: if the browsing context's only entry in its session history is the about:blank Document that was added when the browsing context was created, and navigation is occurring with replacement enabled, and that Document has the same origin as the new Document, then use the Window object of that Document instead, and change the document attribute of the Window object to point to the new Document.

    2. Set the Window object's HTTPS state to the HTTPS state of the resource used to generate the document.

    3. Set the document's referrer to the address of the resource from which Request-URIs are obtained as determined when the fetch algorithm obtained the resource, if that algorithm was used and determined such a value; otherwise, set it to the empty string.

    4. Implement the sandboxing for the Document.

    5. If the active sandboxing flag set of the Document's browsing context or any of its ancestor browsing contexts (if any) have the sandboxed fullscreen browsing context flag set, then skip this step.

       If the Document's browsing context has a browsing context container and either it is not an iframe element, or it does not have the allowfullscreen attribute specified, or its Document does not have the fullscreen enabled flag set, then also skip this step.

       Otherwise, set the Document's fullscreen enabled flag.

25. Non-document content: If, given type, the new resource is to be handled by displaying some sort of inline content, e.g. a native rendering of the content, an error message because the specified type is not supported, or an inline prompt to allow the user to select a registered handler for the given type, then display the inline content, and then abort these steps.

    In the case of a registered handler being used, the algorithm will be reinvoked with a new URL to handle the request.

26. Otherwise, the document's type is such that the resource will not affect the browsing context, e.g. because the resource is to be handed to an external application or because it is an unknown type that will be processed as a download. Process the resource appropriately.

When a resource is handled by passing its URL or data to an external software package separate from the user agent (e.g. handing a mailto: URL to a mail client, or a Word document to a word processor), user agents should attempt to mitigate the risk that this is an attempt to exploit the target software, e.g. by prompting the user to confirm that the source browsing context's active document's origin is to be allowed to invoke the specified software. In particular, if the navigate algorithm, when it was invoked, was not allowed to show a popup, the user agent should not invoke the external software package without prior user confirmation.

For example, there could be a vulnerability in the target software's URL handler which a hostile page would attempt to exploit by tricking a user into clicking a link.

Some of the sections below, to which the above algorithm defers in certain cases, require the user agent to update the session history with the new page. When a user agent is required to do this, it must queue a task (associated with the Document object of the current entry, not the new one) to run the following steps:

1. Unload the Document object of the current entry, with the recycle parameter set to false.

   If this instance of the navigation algorithm is canceled while this step is running the unload a document algorithm, then the unload a document algorithm must be allowed to run to completion, but this instance of the navigation algorithm must not run beyond this step. (In particular, for instance, the cancelation of this algorithm does not abort any event dispatch or script execution occurring as part of unloading the document or its descendants.)

2. If the navigation was initiated for entry update of an entry

   1. Replace the Document of the entry being updated, and any other entries that referenced the same document as that entry, with the new Document.

   2. Traverse the history to the new entry.

   This can only happen if the entry being updated is not the current entry, and can never happen with replacement enabled. (It happens when the user tried to traverse to a session history entry that no longer had a Document object.)

   Otherwise

   1. Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.

      This doesn't necessarily have to affect the user agent's user interface.

   2. Append a new entry at the end of the History object representing the new resource and its Document object and related state.

   3. Traverse the history to the new entry. If the navigation was initiated with replacement enabled, then the traversal must itself be initiated with replacement enabled.

3. The navigation algorithm has now matured.

4. Fragment identifier loop: Spin the event loop for a user-agent-defined amount of time, as desired by the user agent implementor. (This is intended to allow the user agent to optimise the user experience in the face of performance concerns.)

5. If the Document object has no parser, or its parser has stopped parsing, or the user agent has reason to believe the user is no longer interested in scrolling to the fragment identifier, then abort these steps.

6. Scroll to the fragment identifier given in the document's address. If this fails to find an indicated part of the document, then return to the fragment identifier loop step.

The task source for this task is the networking task source.

6.6.2 Page load processing model for HTML files

When an HTML document is to be loaded in a browsing context, the user agent must queue a task to create a Document object, mark it as being an HTML document, set its content type to "text/html", initialise the Document object, and finally create an HTML parser and associate it with the Document. Each task that the networking task source places on the task queue while fetching runs must then fill the parser's input byte stream with the fetched bytes and cause the HTML parser to perform the appropriate processing of the input stream.

The input byte stream converts bytes into characters for use in the tokenizer. This process relies, in part, on character encoding information found in the real Content-Type metadata of the resource; the "sniffed type" is not used for this purpose.

When no more bytes are available, the user agent must queue a task for the parser to process the implied EOF character, which eventually causes a load event to be fired.

After creating the Document object, but before any script execution, certainly before the parser stops, the user agent must update the session history with the new page.

Application cache selection happens in the HTML parser.

The task source for the two tasks mentioned in this section must be the networking task source.

6.6.3 Page load processing model for XML files

When faced with displaying an XML file inline, user agents must follow the requirements defined in the XML and Namespaces in XML recommendations, RFC 7303, DOM, and other relevant specifications to create a Document object and a corresponding XML parser. [XML] [XMLNS] [RFC7303] [DOM]

At the time of writing, the XML specification community had not actually yet specified how XML and the DOM interact.

After the Document is created, the user agent must initialise the Document object.

The actual HTTP headers and other metadata, not the headers as mutated or implied by the algorithms given in this specification, are the ones that must be used when determining the character encoding according to the rules given in the above specifications. Once the character encoding is established, the document's character encoding must be set to that character encoding.

If the root element, as parsed according to the XML specifications cited above, is found to be an html element with an attribute manifest whose value is not the empty string, then, as soon as the element is inserted into the document, the user agent must resolve the value of that attribute relative to that element, and if that is successful, must apply the URL serialiser algorithm to the resulting parsed URL with the exclude fragment flag set to obtain manifest URL, and then run the application cache selection algorithm with manifest URL as the manifest URL, passing in the newly-created Document. Otherwise, if the attribute is absent, its value is the empty string, or resolving its value fails, then as soon as the root element is inserted into the document, the user agent must run the application cache selection algorithm with no manifest, and passing in the Document.

Because the processing of the manifest attribute happens only once the root element is parsed, any URLs referenced by processing instructions before the root element (such as <?xml-stylesheet?> PIs) will be fetched from the network and cannot be cached.

User agents may examine the namespace of the root Element node of this Document object to perform namespace-based dispatch to alternative processing tools, e.g. determining that the content is actually a syndication feed and passing it to a feed handler. If such processing is to take place, abort the steps in this section, and jump to the next step (labeled non-document content) in the navigate steps above.

Otherwise, then, with the newly created Document, the user agent must update the session history with the new page. User agents may do this before the complete document has been parsed (thus achieving incremental rendering), and must do this before any scripts are to be executed.

Error messages from the parse process (e.g. XML namespace well-formedness errors) may be reported inline by mutating the Document.

6.6.4 Page load processing model for text files

When a plain text document is to be loaded in a browsing context, the user agent must queue a task to create a Document object, mark it as being an HTML document, set its content type to the sniffed MIME type of the resource (type in the navigate algorithm), initialise the Document object, create an HTML parser, associate it with the Document, act as if the tokenizer had emitted a start tag token with the tag name "pre" followed by a single U+000A LINE FEED (LF) character, and switch the HTML parser's tokenizer to the PLAINTEXT state. Each task that the networking task source places on the task queue while fetching runs must then fill the parser's input byte stream with the fetched bytes and cause the HTML parser to perform the appropriate processing of the input stream.

The rules for how to convert the bytes of the plain text document into actual characters, and the rules for actually rendering the text to the user, are defined by the specifications for the sniffed MIME type of the resource (type in the navigate algorithm).

The document's character encoding must be set to the character encoding used to decode the document.

Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and passing in the newly-created Document.

When no more bytes are available, the user agent must queue a task for the parser to process the implied EOF character, which eventually causes a load event to be fired.

After creating the Document object, but potentially before the page has finished parsing, the user agent must update the session history with the new page.

User agents may add content to the head element of the Document, e.g. linking to a style sheet or a binding, providing script, giving the document a title, etc.

In particular, if the user agent supports the Format=Flowed feature of RFC 3676 then the user agent would need to apply extra styling to cause the text to wrap correctly and to handle the quoting feature. This could be performed using, e.g., a binding or a CSS extension.

The task source for the two tasks mentioned in this section must be the networking task source.

6.6.5 Page load processing model for multipart/x-mixed-replace resources

When a resource with the type multipart/x-mixed-replace is to be loaded in a browsing context, the user agent must parse the resource using the rules for multipart types. [RFC2046]

For each body part obtained from the resource, the user agent must run a new instance of the navigate algorithm, starting from the resource handling step, using the new body part as the resource being navigated, with replacement enabled if a previous body part from the same resource resulted in a Document object being created and initialised, and otherwise using the same setup as the navigate attempt that caused this section to be invoked in the first place.

For the purposes of algorithms processing these body parts as if they were complete stand-alone resources, the user agent must act as if there were no more bytes for those resources whenever the boundary following the body part is reached.

Thus, load events (and for that matter unload events) do fire for each body part loaded.

6.6.6 Page load processing model for media

When an image, video, or audio resource is to be loaded in a browsing context, the user agent should create a Document object, mark it as being an HTML document, set its content type to the sniffed MIME type of the resource (type in the navigate algorithm), initialise the Document object, append an html element to the Document, append a head element and a body element to the html element, append an element host element for the media, as described below, to the body element, and set the appropriate attribute of the element host element, as described below, to the address of the image, video, or audio resource.

The element host element to create for the media is the element given in the table below in the second cell of the row whose first cell describes the media. The appropriate attribute to set is the one given by the third cell in that same row.

Then, the user agent must act as if it had stopped parsing.

Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and passing in the newly-created Document.

After creating the Document object, but potentially before the page has finished fully loading, the user agent must update the session history with the new page.

User agents may add content to the head element of the Document, or attributes to the element host element, e.g. to link to a style sheet or a binding, to provide a script, to give the document a title, to make the media autoplay, etc.

6.6.7 Page load processing model for content that uses plugins

When a resource that requires an external resource to be rendered is to be loaded in a browsing context, the user agent should create a Document object, mark it as being an HTML document and mark it as being a plugin document, set its content type to the sniffed MIME type of the resource (type in the navigate algorithm), initialise the Document object, append an html element to the Document, append a head element and a body element to the html element, append an embed to the body element, and set the src attribute of the embed element to the address of the resource.

The term plugin document is used by Content Security Policy as part of the mechanism that ensures iframes can't be used to evade plugin-types directives. [CSP]

Then, the user agent must act as if it had stopped parsing.

Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and passing in the newly-created Document.

After creating the Document object, but potentially before the page has finished fully loading, the user agent must update the session history with the new page.

User agents may add content to the head element of the Document, or attributes to the embed element, e.g. to link to a style sheet or a binding, or to give the document a title.

If the Document's active sandboxing flag set has its sandboxed plugins browsing context flag set, the synthesized embed element will fail to render the content if the relevant plugin cannot be secured.

6.6.8 Page load processing model for inline content that doesn't have a DOM

When the user agent is to display a user agent page inline in a browsing context, the user agent should create a Document object, mark it as being an HTML document, set its content type to "text/html", initialise the Document object, and then either associate that Document with a custom rendering that is not rendered using the normal Document rendering rules, or mutate that Document until it represents the content the user agent wants to render.

Once the page has been set up, the user agent must act as if it had stopped parsing.

Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, passing in the newly-created Document.

After creating the Document object, but potentially before the page has been completely set up, the user agent must update the session history with the new page.

6.6.9 Navigating to a fragment identifier

When a user agent is supposed to navigate to a fragment identifier, then the user agent must run the following steps:

1. Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.

   This doesn't necessarily have to affect the user agent's user interface.

2. Remove any tasks queued by the history traversal task source that are associated with any Document objects in the top-level browsing context's document family.

3. Append a new entry at the end of the History object representing the new resource and its Document object and related state. Its URL must be set to the address to which the user agent was navigating. The title must be left unset.

4. Traverse the history to the new entry, with the non-blocking events flag set. This will scroll to the fragment identifier given in what is now the document's address.

If the scrolling fails because the relevant ID has not yet been parsed, then the original navigation algorithm will take care of the scrolling instead, as the last few steps of its update the session history with the new page algorithm.

When the user agent is required to scroll to the fragment identifier and the indicated part of the document, if any, is being rendered, the user agent must either change the scrolling position of the document using the following algorithm, or perform some other action such that the indicated part of the document is brought to the user's attention. If there is no indicated part, or if the indicated part is not being rendered, then the user agent must do nothing. The aforementioned algorithm is as follows:

1. Let target be the indicated part of the document, as defined below.

2. If target is the top of the document, then scroll to the beginning of the document for the Document, and abort these steps. [CSSOMVIEW]

3. Use the scroll an element into view algorithm to scroll target into view, with the align to top flag set. [CSSOMVIEW]

4. Run the focusing steps for that element, with the Document's viewport as the fallback target.

5. Optionally, move the sequential focus navigation starting point to target.

The indicated part of the document is the one that the fragment identifier, if any, identifies. The semantics of the fragment identifier in terms of mapping it to a specific DOM Node is defined by the specification that defines the MIME type used by the Document (for example, the processing of fragment identifiers for XML MIME types is the responsibility of RFC7303). [RFC7303]

For HTML documents (and HTML MIME types), the following processing model must be followed to determine what the indicated part of the document is.

1. Apply the URL parser algorithm to the URL, and let fragid be the fragment component of the resulting parsed URL.

2. If fragid is the empty string, then the indicated part of the document is the top of the document; stop the algorithm here.

3. Let fragid bytes be the result of percent-decoding fragid.

4. Let decoded fragid be the result of applying the UTF-8 decoder algorithm to fragid bytes. If the UTF-8 decoder emits a decoder error, abort the decoder and instead jump to the step labeled no decoded fragid.

5. If there is an element in the DOM that has an ID exactly equal to decoded fragid, then the first such element in tree order is the indicated part of the document; stop the algorithm here.

6. No decoded fragid: If there is an a element in the DOM that has a name attribute whose value is exactly equal to fragid (not decoded fragid), then the first such element in tree order is the indicated part of the document; stop the algorithm here.

7. If fragid is an ASCII case-insensitive match for the string top, then the indicated part of the document is the top of the document; stop the algorithm here.

8. Otherwise, there is no indicated part of the document.

For the purposes of the interaction of HTML with Selectors' :target pseudo-class, the target element is the indicated part of the document, if that is an element; otherwise there is no target element. [SELECTORS]

The task source for the task mentioned in this section must be the DOM manipulation task source.

6.6.10 History traversal

When a user agent is required to traverse the history to a specified entry, optionally with replacement enabled, and optionally with the non-blocking events flag set, the user agent must act as follows.

This algorithm is not just invoked when explicitly going back or forwards in the session history — it is also invoked in other situations, for example when navigating a browsing context, as part of updating the session history with the new page.

1. If there is no longer a Document object for the entry in question, navigate the browsing context to the resource for that entry to perform an entry update of that entry, and abort these steps. The "navigate" algorithm reinvokes this "traverse" algorithm to complete the traversal, at which point there is a Document object and so this step gets skipped. The navigation must be done using the same source browsing context as was used the first time this entry was created. (This can never happen with replacement enabled.)

   If the resource was obtained using a non-idempotent action, for example a POST form submission, or if the resource is no longer available, for example because the computer is now offline and the page wasn't cached, navigating to it again might not be possible. In this case, the navigation will result in a different page than previously; for example, it might be an error message explaining the problem or offering to resubmit the form.

2. If the current entry's title was not set by the pushState() or replaceState() methods, then set its title to the value returned by the document.title IDL attribute.

3. If appropriate, update the current entry in the browsing context's Document object's History object to reflect any state that the user agent wishes to persist. The entry is then said to be an entry with persisted user state.

4. If the specified entry has a different Document object than the current entry, then run the following substeps:

   1. Remove any tasks queued by the history traversal task source that are associated with any Document objects in the top-level browsing context's document family.

   2. If the origin of the Document of the specified entry is not the same as the origin of the Document of the current entry, then run the following sub-sub-steps:

      1. The current browsing context name must be stored with all the entries in the history that are associated with Document objects with the same origin as the active document and that are contiguous with the current entry.

      2. If the browsing context is a top-level browsing context, but not an auxiliary browsing context, then the browsing context's browsing context name must be unset.

   3. Make the specified entry's Document object the active document of the browsing context.

   4. If the specified entry has a browsing context name stored with it, then run the following sub-sub-steps:

      1. Set the browsing context's browsing context name to the name stored with the specified entry.

      2. Clear any browsing context names stored with all entries in the history that are associated with Document objects with the same origin as the new active document and that are contiguous with the specified entry.

   5. If the specified entry's Document has any form controls whose autofill field name is "off", invoke the reset algorithm of each of those elements.

   6. If the current document readiness of the specified entry's Document is "complete", queue a task to run the following sub-sub-steps:

      1. If the Document's page showing flag is true, then abort this task (i.e. don't fire the event below).

      2. Set the Document's page showing flag to true.

      3. Run any session history document visibility change steps for Document that are defined by other applicable specifications.

         This is specifically intended for use by the Page Visibility specification. [PAGEVIS]

      4. Fire a trusted event with the name pageshow at the Window object of that Document, with target override set to the Document object, using the PageTransitionEvent interface, with the persisted attribute initialised to true. This event must not bubble, must not be cancelable, and has no default action.

5. Set the document's address to the URL of the specified entry.

6. If the specified entry has a URL whose fragment identifier differs from that of the current entry's when compared in a case-sensitive manner, and the two share the same Document object, then let hash changed be true, and let old URL be the URL of the current entry and new URL be the URL of the specified entry. Otherwise, let hash changed be false.

7. If the traversal was initiated with replacement enabled, remove the entry immediately before the specified entry in the session history.

8. If the specified entry is not an entry with persisted user state, but its URL has a fragment identifier, scroll to the fragment identifier.

9. If the entry is an entry with persisted user state, the user agent may update aspects of the document and its rendering, for instance the scroll position or values of form fields, that it had previously recorded.

   This can even include updating the dir attribute of textarea elements or input elements whose type attribute is in either the Text state or the Search state, if the persisted state includes the directionality of user input in such controls.

10. If the entry is a state object entry, let state be a structured clone of that state object. Otherwise, let state be null.

11. Set history.state to state.

12. Let state changed be true if the Document of the specified entry has a latest entry, and that entry is not the specified entry; otherwise let it be false.

13. Let the latest entry of the Document of the specified entry be the specified entry.

14. If the non-blocking events flag is not set, then run the following steps immediately. Otherwise, the non-blocking events flag is set; queue a task to run the following substeps instead.

    1. If state changed is true, fire a trusted event with the name popstate at the Window object of the Document, using the PopStateEvent interface, with the state attribute initialised to the value of state. This event must bubble but not be cancelable and has no default action.

    2. If hash changed is true, then fire a trusted event with the name hashchange at the browsing context's Window object, using the HashChangeEvent interface, with the oldURL attribute initialised to old URL and the newURL attribute initialised to new URL. This event must bubble but not be cancelable and has no default action.

15. The current entry is now the specified entry.

The task source for the tasks mentioned above is the DOM manipulation task source.

[Constructor(DOMString type, optional PopStateEventInit eventInitDict), Exposed=(Window,Worker)]
interface PopStateEvent : Event {
  readonly attribute any state;
};

dictionary PopStateEventInit : EventInit {
  any state;
};

[Constructor(DOMString type, optional HashChangeEventInit eventInitDict), Exposed=(Window,Worker)]
interface HashChangeEvent : Event {
  readonly attribute DOMString oldURL;
  readonly attribute DOMString newURL;
};

dictionary HashChangeEventInit : EventInit {
  DOMString oldURL;
  DOMString newURL;
};

[Constructor(DOMString type, optional PageTransitionEventInit eventInitDict), Exposed=(Window,Worker)]
interface PageTransitionEvent : Event {
  readonly attribute boolean persisted;
};

dictionary PageTransitionEventInit : EventInit {
  boolean persisted;
};

6.6.11 Unloading documents

A Document has a salvageable state, which must initially be true, a fired unload flag, which must initially be false, and a page showing flag, which must initially be false. The page showing flag is used to ensure that scripts receive pageshow and pagehide events in a consistent manner (e.g. that they never receive two pagehide events in a row without an intervening pageshow, or vice versa).

Event loops have a termination nesting level counter, which must initially be zero.

When a user agent is to prompt to unload a document, it must run the following steps.

1. Increase the event loop's termination nesting level by one.

2. Increase the Document's ignore-opens-during-unload counter by one.

3. Let event be a new trusted BeforeUnloadEvent event object with the name beforeunload, which does not bubble but is cancelable.

4. Dispatch: Dispatch event at the Document's Window object.

5. Decrease the event loop's termination nesting level by one.

6. Release the storage mutex.

7. If any event listeners were triggered by the earlier dispatch step, then set the Document's salvageable state to false.

8. If the Document's active sandboxing flag set does not have its sandboxed modals flag set, and the returnValue attribute of the event object is not the empty string, or if the event was canceled, then the user agent should ask the user to confirm that they wish to unload the document.

   The prompt shown by the user agent may include the string of the returnValue attribute, or some leading subset thereof. (A user agent may want to truncate the string to 1024 characters for display, for instance.)

   The user agent must pause while waiting for the user's response.

   If the user did not confirm the page navigation, then the user agent refused to allow the document to be unloaded.

9. If this algorithm was invoked by another instance of the "prompt to unload a document" algorithm (i.e. through the steps below that invoke this algorithm for all descendant browsing contexts), then jump to the step labeled end.

10. Let descendants be the list of the descendant browsing contexts of the Document.

11. If descendants is not an empty list, then for each browsing context b in descendants run the following substeps:

    1. Prompt to unload the active document of the browsing context b. If the user refused to allow the document to be unloaded, then the user implicitly also refused to allow this document to be unloaded; jump to the step labeled end.

    2. If the salvageable state of the active document of the browsing context b is false, then set the salvageable state of this document to false also.

12. End: Decrease the Document's ignore-opens-during-unload counter by one.

When a user agent is to unload a document, it must run the following steps. These steps are passed an argument, recycle, which is either true or false, indicating whether the Document object is going to be re-used. (This is set by the document.open() method.)

1. Increase the event loop's termination nesting level by one.

2. Increase the Document's ignore-opens-during-unload counter by one.

3. If the Document's page showing flag is false, then jump to the step labeled unload event below (i.e. skip firing the pagehide event and don't rerun the unloading document visibility change steps).

4. Set the Document's page showing flag to false.

5. Fire a trusted event with the name pagehide at the Window object of the Document, with target override set to the Document object, using the PageTransitionEvent interface, with the persisted attribute initialised to true if the Document object's salvageable state is true, and false otherwise. This event must not bubble, must not be cancelable, and has no default action.

6. Run any unloading document visibility change steps for Document that are defined by other applicable specifications.

   This is specifically intended for use by the Page Visibility specification. [PAGEVIS]

7. Unload event: If the Document's fired unload flag is false, fire a simple event named unload at the Document's Window object, with target override set to the Document object.

8. Decrease the event loop's termination nesting level by one.

9. Release the storage mutex.

10. If any event listeners were triggered by the earlier unload event step, then set the Document object's salvageable state to false and set the Document's fired unload flag to true.

11. Run any unloading document cleanup steps for Document that are defined by this specification and other applicable specifications.

12. If this algorithm was invoked by another instance of the "unload a document" algorithm (i.e. by the steps below that invoke this algorithm for all descendant browsing contexts), then jump to the step labeled end.

13. Let descendants be the list of the descendant browsing contexts of the Document.

14. If descendants is not an empty list, then for each browsing context b in descendants run the following substeps:

    1. Unload the active document of the browsing context b with the recycle parameter set to false.

    2. If the salvageable state of the active document of the browsing context b is false, then set the salvageable state of this document to false also.

15. If both the Document's salvageable state and recycle are false, then the Document's browsing context must discard the Document.

16. End: Decrease the Document's ignore-opens-during-unload counter by one.

This specification defines the following unloading document cleanup steps. Other specifications can define more.

1. Make disappear any WebSocket objects that were created by the WebSocket() constructor from the Document's Window object.

   If this affected any WebSocket objects, then set Document's salvageable state to false.

2. If the Document's salvageable state is false, forcibly close any EventSource objects that whose constructor was invoked from the Document's Window object.

3. If the Document's salvageable state is false, empty the Document's Window's list of active timers.

interface BeforeUnloadEvent : Event {
  attribute DOMString returnValue;
};

6.6.12 Aborting a document load

If a Document is aborted, the user agent must run the following steps:

1. Abort the active documents of every child browsing context. If this results in any of those Document objects having their salvageable state set to false, then set this Document's salvageable state to false also.

2. Cancel any instances of the fetch algorithm in the context of this Document, discarding any tasks queued for them, and discarding any further data received from the network for them. If this resulted in any instances of the fetch algorithm being canceled or any queued tasks or any network data getting discarded, then set the Document's salvageable state to false.

3. If the Document has an active parser, then abort that parser and set the Document's salvageable state to false.

User agents may allow users to explicitly invoke the abort a document algorithm for a Document. If the user does so, then, if that Document is an active document, the user agent should queue a task to fire a simple event named abort at that Document's Window object before invoking the abort algorithm.

6.7.1 Introduction

This section is non-normative.

In order to enable users to continue interacting with Web applications and documents even when their network connection is unavailable — for instance, because they are traveling outside of their ISP's coverage area — authors can provide a manifest which lists the files that are needed for the Web application to work offline and which causes the user's browser to keep a copy of the files for use offline.

To illustrate this, consider a simple clock applet consisting of an HTML page "clock.html", a CSS style sheet "clock.css", and a JavaScript script "clock.js".

Before adding the manifest, these three files might look like this:

<!-- clock.html -->
<!DOCTYPE HTML>
<html>
 <head>
  <title>Clock</title>
  <script src="clock.js"></script>
  <link rel="stylesheet" href="clock.css">
 </head>
 <body>
  <p>The time is: <output id="clock"></output></p>
 </body>
</html>

/* clock.css */
output { font: 2em sans-serif; }

/* clock.js */
setInterval(function () {
    document.getElementById('clock').value = new Date();
}, 1000);

If the user tries to open the "clock.html" page while offline, though, the user agent (unless it happens to have it still in the local cache) will fail with an error.

The author can instead provide a manifest of the three files, say "clock.appcache":

CACHE MANIFEST
clock.html
clock.css
clock.js

With a small change to the HTML file, the manifest (served as text/cache-manifest) is linked to the application:

<!-- clock.html -->
<!DOCTYPE HTML>
<html manifest="clock.appcache">
 <head>
  <title>Clock</title>
  <script src="clock.js"></script>
  <link rel="stylesheet" href="clock.css">
 </head>
 <body>
  <p>The time is: <output id="clock"></output></p>
 </body>
</html>

Now, if the user goes to the page, the browser will cache the files and make them available even when the user is offline.

Authors are encouraged to include the main page in the manifest also, but in practice the page that referenced the manifest is automatically cached even if it isn't explicitly mentioned.

With the exception of "no-store" directive, HTTP cache headers and restrictions on caching pages served over TLS (encrypted, using https:) are overridden by manifests. Thus, pages will not expire from an application cache before the user agent has updated it, and even applications served over TLS can be made to work offline.

View this example online.

SETTINGS:
prefer-online
NETWORK:
*

6.7.2 Application caches

An application cache is a set of cached resources consisting of:

• One or more resources (including their out-of-band metadata, such as HTTP headers, if any), identified by URLs, each falling into one (or more) of the following categories:

  Master entries

  These are documents that were added to the cache because a browsing context was navigated to that document and the document indicated that this was its cache, using the manifest attribute.

  The manifest

  This is the resource corresponding to the URL that was given in a master entry's html element's manifest attribute. The manifest is fetched and processed during the application cache download process. All the master entries have the same origin as the manifest.

  Explicit entries

  These are the resources that were listed in the cache's manifest in an explicit section.

  Fallback entries

  These are the resources that were listed in the cache's manifest in a fallback section.

  Explicit entries and Fallback entries can be marked as foreign, which means that they have a manifest attribute but that it doesn't point at this cache's manifest.

  A URL in the list can be flagged with multiple different types, and thus an entry can end up being categorised as multiple entries. For example, an entry can be a manifest entry and an explicit entry at the same time, if the manifest is listed within the manifest.

• Zero or more fallback namespaces, each of which is mapped to a fallback entry.

  These are URLs used as prefix match patterns for resources that are to be fetched from the network if possible, or to be replaced by the corresponding fallback entry if not. Each namespace URL has the same origin as the manifest.

• Zero or more URLs that form the online whitelist namespaces.

  These are used as prefix match patterns, and declare URLs for which the user agent will ignore the application cache, instead fetching them normally (i.e. from the network or local HTTP cache as appropriate).

• An online whitelist wildcard flag, which is either open or blocking.

  The open state indicates that any URL not listed as cached is to be implicitly treated as being in the online whitelist namespaces; the blocking state indicates that URLs not listed explicitly in the manifest are to be treated as unavailable.

• A cache mode flag, which is either in the fast state or the prefer-online state.

Each application cache has a completeness flag, which is either complete or incomplete.

An application cache group is a group of application caches, identified by the absolute URL of a resource manifest which is used to populate the caches in the group.

An application cache is newer than another if it was created after the other (in other words, application caches in an application cache group have a chronological order).

Only the newest application cache in an application cache group can have its completeness flag set to incomplete; the others are always all complete.

Each application cache group has an update status, which is one of the following: idle, checking, downloading.

A relevant application cache is an application cache that is the newest in its group to be complete.

Each application cache group has a list of pending master entries. Each entry in this list consists of a resource and a corresponding Document object. It is used during the application cache download process to ensure that new master entries are cached even if the application cache download process was already running for their application cache group when they were loaded.

An application cache group can be marked as obsolete, meaning that it must be ignored when looking at what application cache groups exist.

A cache host is a Document or a SharedWorkerGlobalScope object. A cache host can be associated with an application cache.

A Document initially is not associated with an application cache, but can become associated with one early during the page load process, when steps in the parser and in the navigation sections cause cache selection to occur.

A SharedWorkerGlobalScope can be associated with an application cache when it is created.

Each cache host has an associated ApplicationCache object.

Multiple application caches in different application cache groups can contain the same resource, e.g. if the manifests all reference that resource. If the user agent is to select an application cache from a list of relevant application caches that contain a resource, the user agent must use the application cache that the user most likely wants to see the resource from, taking into account the following:

• which application cache was most recently updated,
• which application cache was being used to display the resource from which the user decided to look at the new resource, and
• which application cache the user prefers.

A URL matches a fallback namespace if there exists a relevant application cache whose manifest's URL has the same origin as the URL in question, and that has a fallback namespace that is a prefix match for the URL being examined. If multiple fallback namespaces match the same URL, the longest one is the one that matches. A URL looking for a fallback namespace can match more than one application cache at a time, but only matches one namespace in each cache.

6.7.3 The cache manifest syntax

CACHE MANIFEST
# the above line is required

# this is a comment
# there can be as many of these anywhere in the file
# they are all ignored
  # comments can have spaces before them
  # but must be alone on the line

# blank lines are ignored too

# these are files that need to be cached they can either be listed
# first, or a "CACHE:" header could be put before them, as is done
# lower down.
images/sound-icon.png
images/background.png
# note that each file has to be put on its own line

# here is a file for the online whitelist -- it isn't cached, and
# references to this file will bypass the cache, always hitting the
# network (or trying to, if the user is offline).
NETWORK:
comm.cgi

# here is another set of files to cache, this time just the CSS file.
CACHE:
style/default.css

CACHE MANIFEST
NETWORK:
comm.cgi
CACHE:
style/default.css
images/sound-icon.png
images/background.png

CACHE MANIFEST

/main/home
/main/app.js
/settings/home
/settings/app.js
http://img.example.com/logo.png
http://img.example.com/check.png
http://img.example.com/cross.png

CACHE MANIFEST
FALLBACK:
/ /offline.html
NETWORK:
*

6.7.4 Downloading or updating an application cache

When the user agent is required (by other parts of this specification) to start the application cache download process for an absolute URL purported to identify a manifest, or for an application cache group, potentially given a particular cache host, and potentially given a master resource, the user agent must run the steps below. These steps are always run in parallel with the event loop tasks.

Some of these steps have requirements that only apply if the user agent shows caching progress. Support for this is optional. Caching progress UI could consist of a progress bar or message panel in the user agent's interface, or an overlay, or something else. Certain events fired during the application cache download process allow the script to override the display of such an interface. (Such events are delayed until after the load event has fired.) The goal of this is to allow Web applications to provide more seamless update mechanisms, hiding from the user the mechanics of the application cache mechanism. User agents may display user interfaces independent of this, but are encouraged to not show prominent update progress notifications for applications that cancel the relevant events.

The application cache download process steps are as follows:

1. Optionally, wait until the permission to start the application cache download process has been obtained from the user and until the user agent is confident that the network is available. This could include doing nothing until the user explicitly opts-in to caching the site, or could involve prompting the user for permission. The algorithm might never get past this point. (This step is particularly intended to be used by user agents running on severely space-constrained devices or in highly privacy-sensitive environments).

2. Atomically, so as to avoid race conditions, perform the following substeps:

   1. Pick the appropriate substeps:

      If these steps were invoked with an absolute URL purported to identify a manifest

      Let manifest URL be that absolute URL.

      If there is no application cache group identified by manifest URL, then create a new application cache group identified by manifest URL. Initially, it has no application caches. One will be created later in this algorithm.

      If these steps were invoked with an application cache group

      Let manifest URL be the absolute URL of the manifest used to identify the application cache group to be updated.

      If that application cache group is obsolete, then abort this instance of the application cache download process. This can happen if another instance of this algorithm found the manifest to be 404 or 410 while this algorithm was waiting in the first step above.

   2. Let cache group be the application cache group identified by manifest URL.

   3. If these steps were invoked with a master resource, then add the resource, along with the resource's Document, to cache group's list of pending master entries.

   4. If these steps were invoked with a cache host, and the status of cache group is checking or downloading, then queue a post-load task to fire a simple event named checking that is cancelable at the ApplicationCache singleton of that cache host. The default action of this event must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the user agent is checking to see if it can download the application.

   5. If these steps were invoked with a cache host, and the status of cache group is downloading, then also queue a post-load task to fire a simple event named downloading that is cancelable at the ApplicationCache singleton of that cache host. The default action of this event must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user the application is being downloaded.

   6. If the status of the cache group is either checking or downloading, then abort this instance of the application cache download process, as an update is already in progress.

   7. Set the status of cache group to checking.

   8. For each cache host associated with an application cache in cache group, queue a post-load task to fire a simple event that is cancelable named checking at the ApplicationCache singleton of the cache host. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the user agent is checking for the availability of updates.

   The remainder of the steps run in parallel.

   If cache group already has an application cache in it, then this is an upgrade attempt. Otherwise, this is a cache attempt.

3. If this is a cache attempt, then this algorithm was invoked with a cache host; queue a post-load task to fire a simple event named checking that is cancelable at the ApplicationCache singleton of that cache host. The default action of this event must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the user agent is checking for the availability of updates.

4. Let request be a new request whose url is manifest URL, client is null, destination is "subresource", omit-Origin-header flag is set, referrer is "no-referrer", synchronous flag is set, credentials mode is "include", and whose use-URL-credentials flag is set.

5. Fetching the manifest: Let manifest be the result of fetching request. HTTP caching semantics should be honored for this request.

   Parse manifest's body according to the rules for parsing manifests, obtaining a list of explicit entries, fallback entries and the fallback namespaces that map to them, entries for the online whitelist, and values for the online whitelist wildcard flag and the cache mode flag.

   The MIME type of the resource is ignored — it is assumed to be text/cache-manifest. In the future, if new manifest formats are supported, the different types will probably be distinguished on the basis of the file signatures (for the current format, that is the "CACHE MANIFEST" string at the top of the file).

6. If fetching the manifest fails due to a 404 or 410 response status, then run these substeps:

   1. Mark cache group as obsolete. This cache group no longer exists for any purpose other than the processing of Document objects already associated with an application cache in the cache group.

   2. Let task list be an empty list of tasks.

   3. For each cache host associated with an application cache in cache group, create a task to fire a simple event named obsolete that is cancelable at the ApplicationCache singleton of the cache host, and append it to task list. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the application is no longer available for offline use.

   4. For each entry in cache group's list of pending master entries, create a task to fire a simple event that is cancelable named error (not obsolete!) at the ApplicationCache singleton of the Document for this entry, if there still is one, and append it to task list. The default action of this event must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

   5. If cache group has an application cache whose completeness flag is incomplete, then discard that application cache.

   6. If appropriate, remove any user interface indicating that an update for this cache is in progress.

   7. Let the status of cache group be idle.

   8. For each task in task list, queue that task as a post-load task.

   9. Abort the application cache download process.

7. Otherwise, if fetching the manifest fails in some other way (e.g. the server returns another 4xx or 5xx response, or there is a DNS error, or the connection times out, or the user cancels the download, or the parser for manifests fails when checking the magic signature), or if the server returned a redirect, then run the cache failure steps. [HTTP]

8. If this is an upgrade attempt and the newly downloaded manifest is byte-for-byte identical to the manifest found in the newest application cache in cache group, or the response status is 304, then run these substeps:

   1. Let cache be the newest application cache in cache group.

   2. Let task list be an empty list of tasks.

   3. For each entry in cache group's list of pending master entries, wait for the resource for this entry to have either completely downloaded or failed.

      If the download failed (e.g. the server returns a 4xx or 5xx response, or there is a DNS error, the connection times out, or the user cancels the download), or if the resource is labeled with the "no-store" cache directive, then create a task to fire a simple event that is cancelable named error at the ApplicationCache singleton of the Document for this entry, if there still is one, and append it to task list. The default action of this event must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

      Otherwise, associate the Document for this entry with cache; store the resource for this entry in cache, if it isn't already there, and categorise its entry as a master entry. If applying the URL parser algorithm to the resource's URL results in a parsed URL that has a non-null fragment component, the URL used for the entry in cache must instead be the absolute URL obtained from applying the URL serialiser algorithm to the parsed URL with the exclude fragment flag set (application caches never include fragment identifiers).

   4. For each cache host associated with an application cache in cache group, create a task to fire a simple event that is cancelable named noupdate at the ApplicationCache singleton of the cache host, and append it to task list. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the application is up to date.

   5. Empty cache group's list of pending master entries.

   6. If appropriate, remove any user interface indicating that an update for this cache is in progress.

   7. Let the status of cache group be idle.

   8. For each task in task list, queue that task as a post-load task.

   9. Abort the application cache download process.

9. Let new cache be a newly created application cache in cache group. Set its completeness flag to incomplete.

10. For each entry in cache group's list of pending master entries, associate the Document for this entry with new cache.

11. Set the status of cache group to downloading.

12. For each cache host associated with an application cache in cache group, queue a post-load task to fire a simple event that is cancelable named downloading at the ApplicationCache singleton of the cache host. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that a new version is being downloaded.

13. Let file list be an empty list of URLs with flags.

14. Add all the URLs in the list of explicit entries obtained by parsing manifest to file list, each flagged with "explicit entry".

15. Add all the URLs in the list of fallback entries obtained by parsing manifest to file list, each flagged with "fallback entry".

16. If this is an upgrade attempt, then add all the URLs of master entries in the newest application cache in cache group whose completeness flag is complete to file list, each flagged with "master entry".

17. If any URL is in file list more than once, then merge the entries into one entry for that URL, that entry having all the flags that the original entries had.

18. For each URL in file list, run the following steps. These steps may be run in parallel for two or more of the URLs at a time. If, while running these steps, the ApplicationCache object's abort() method sends a signal to this instance of the application cache download process algorithm, then run the cache failure steps instead.

    1. If the resource URL being processed was flagged as neither an "explicit entry" nor or a "fallback entry", then the user agent may skip this URL.

       This is intended to allow user agents to expire resources not listed in the manifest from the cache. Generally, implementors are urged to use an approach that expires lesser-used resources first.

    2. For each cache host associated with an application cache in cache group, queue a progress post-load task to fire a trusted event with the name progress, which does not bubble, which is cancelable, and which uses the ProgressEvent interface, at the ApplicationCache singleton of the cache host. The lengthComputable attribute must be set to true, the total attribute must be set to the number of files in file list, and the loaded attribute must be set to the number of files in file list that have been either downloaded or skipped so far. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that a file is being downloaded in preparation for updating the application. [XHR]

    3. Let request be a new request whose url is URL, client is null, destination is "subresource", origin is manifest URL's origin, referrer is "no-referrer", synchronous flag is set, credentials mode is "include", use-URL-credentials flag is set, and redirect mode is "manual".

    4. Fetch request. If this is an upgrade attempt, then use the newest application cache in cache group as an HTTP cache, and honor HTTP caching semantics (such as expiration, ETags, and so forth) with respect to that cache. User agents may also have other caches in place that are also honored.

    5. If the previous step fails (e.g. the server returns a 4xx or 5xx response, or there is a DNS error, or the connection times out, or the user cancels the download), or if the server returned a redirect, or if the resource is labeled with the "no-store" cache directive, then run the first appropriate step from the following list: [HTTP]

       If the URL being processed was flagged as an "explicit entry" or a "fallback entry"

       If these steps are being run in parallel for any other URLs in file list, then abort these steps for those other URLs. Run the cache failure steps.

       Redirects are fatal because they are either indicative of a network problem (e.g. a captive portal); or would allow resources to be added to the cache under URLs that differ from any URL that the networking model will allow access to, leaving orphan entries; or would allow resources to be stored under URLs different than their true URLs. All of these situations are bad.

       If the error was a 404 or 410 HTTP response

       If the resource was labeled with the "no-store" cache directive

       Skip this resource. It is dropped from the cache.

       Otherwise

       Copy the resource and its metadata from the newest application cache in cache group whose completeness flag is complete, and act as if that was the fetched resource, ignoring the resource obtained from the network.

       User agents may warn the user of these errors as an aid to development.

       These rules make errors for resources listed in the manifest fatal, while making it possible for other resources to be removed from caches when they are removed from the server, without errors, and making non-manifest resources survive server-side errors.

       Except for the "no-store" directive, HTTP caching rules that would cause a file to be expired or otherwise not cached are ignored for the purposes of the application cache download process.

    6. Otherwise, the fetching succeeded. Store the resource in the new cache.

       If the user agent is not able to store the resource (e.g. because of quota restrictions), the user agent may prompt the user or try to resolve the problem in some other manner (e.g. automatically pruning content in other caches). If the problem cannot be resolved, the user agent must run the cache failure steps.

    7. If the URL being processed was flagged as an "explicit entry" in file list, then categorise the entry as an explicit entry.

    8. If the URL being processed was flagged as a "fallback entry" in file list, then categorise the entry as a fallback entry.

    9. If the URL being processed was flagged as an "master entry" in file list, then categorise the entry as a master entry.

    10. As an optimization, if the resource is an HTML or XML file whose root element is an html element with a manifest attribute whose value doesn't match the manifest URL of the application cache being processed, then the user agent should mark the entry as being foreign.

19. For each cache host associated with an application cache in cache group, queue a progress post-load task to fire a trusted event with the name progress, which does not bubble, which is cancelable, and which uses the ProgressEvent interface, at the ApplicationCache singleton of the cache host. The lengthComputable attribute must be set to true, the total and the loaded attributes must be set to the number of files in file list. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that all the files have been downloaded. [XHR]

20. Store the list of fallback namespaces, and the URLs of the fallback entries that they map to, in new cache.

21. Store the URLs that form the new online whitelist in new cache.

22. Store the value of the new online whitelist wildcard flag in new cache.

23. Store the value of the new cache mode flag in new cache.

24. For each entry in cache group's list of pending master entries, wait for the resource for this entry to have either completely downloaded or failed.

    If the download failed (e.g. the server returns a 4xx or 5xx response, or there is a DNS error, the connection times out, or the user cancels the download), or if the resource is labeled with the "no-store" cache directive, then run these substeps:

    1. Unassociate the Document for this entry from new cache.

    2. Queue a post-load task to fire a simple event that is cancelable named error at the ApplicationCache singleton of the Document for this entry, if there still is one. The default action of this event must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

    3. If this is a cache attempt and this entry is the last entry in cache group's list of pending master entries, then run these further substeps:

       1. Discard cache group and its only application cache, new cache.

       2. If appropriate, remove any user interface indicating that an update for this cache is in progress.

       3. Abort the application cache download process.

    4. Otherwise, remove this entry from cache group's list of pending master entries.

    Otherwise, store the resource for this entry in new cache, if it isn't already there, and categorise its entry as a master entry.

25. Let request be a new request whose url is manifest URL, client is null, destination is "subresource", referrer is "no-referrer", synchronous flag is set, credentials mode is "include", and whose use-URL-credentials flag is set.

26. Let second manifest be the result of fetching request. HTTP caching semantics should again be honored for this request.

    Since caching can be honored, authors are encouraged to avoid setting the cache headers on the manifest in such a way that the user agent would simply not contact the network for this second request; otherwise, the user agent would not notice if the cache had changed during the cache update process.

27. If the previous step failed for any reason, or if the fetching attempt involved a redirect, or if second manifest and manifest are not byte-for-byte identical, then schedule a rerun of the entire algorithm with the same parameters after a short delay, and run the cache failure steps.

28. Otherwise, store manifest in new cache, if it's not there already, and categorise its entry as the manifest.

29. Set the completeness flag of new cache to complete.

30. Let task list be an empty list of tasks.

31. If this is a cache attempt, then for each cache host associated with an application cache in cache group, create a task to fire a simple event that is cancelable named cached at the ApplicationCache singleton of the cache host, and append it to task list. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the application has been cached and that they can now use it offline.

    Otherwise, it is an upgrade attempt. For each cache host associated with an application cache in cache group, create a task to fire a simple event that is cancelable named updateready at the ApplicationCache singleton of the cache host, and append it to task list. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that a new version is available and that they can activate it by reloading the page.

32. If appropriate, remove any user interface indicating that an update for this cache is in progress.

33. Set the update status of cache group to idle.

34. For each task in task list, queue that task as a post-load task.

The cache failure steps are as follows:

1. Let task list be an empty list of tasks.

2. For each entry in cache group's list of pending master entries, run the following further substeps. These steps may be run in parallel for two or more entries at a time.

   1. Wait for the resource for this entry to have either completely downloaded or failed.

   2. Unassociate the Document for this entry from its application cache, if it has one.

   3. Create a task to fire a simple event that is cancelable named error at the ApplicationCache singleton of the Document for this entry, if there still is one, and append it to task list. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

3. For each cache host still associated with an application cache in cache group, create a task to fire a simple event that is cancelable named error at the ApplicationCache singleton of the cache host, and append it to task list. The default action of these events must be, if the user agent shows caching progress, the display of some sort of user interface indicating to the user that the user agent failed to save the application for offline use.

4. Empty cache group's list of pending master entries.

5. If cache group has an application cache whose completeness flag is incomplete, then discard that application cache.

6. If appropriate, remove any user interface indicating that an update for this cache is in progress.

7. Let the status of cache group be idle.

8. If this was a cache attempt, discard cache group altogether.

9. For each task in task list, queue that task as a post-load task.

10. Abort the application cache download process.