HTML 5.1

When the element is created, if the attribute is absent, the additional information should be hidden; if the attribute is present, that information should be shown. Subsequently, if the attribute is removed, then the information should be hidden; if the attribute is added, the information should be shown.

The user agent should allow the user to request that the additional information be shown or hidden. To honor a request for the details to be shown, the user agent must set the open attribute on the element to the value open. To honor a request for the information to be hidden, the user agent must remove the open attribute from the element.

Whenever the open attribute is added to or removed from a details element, the user agent must queue a task that runs the following steps, which are known as the details notification task steps#details-notification-task-stepsReferenced in:4.11.1. The details element, for this details element:

1. If another task has been queued to run the details notification task steps for this details element, then abort these steps.

   When the open attribute is toggled several times in succession, these steps essentially get coalesced so that only one event is fired.

2. Fire a simple event named toggle at the details element.

The task source for this task must be the DOM manipulation task source.

The open#dom-htmldetailselement-openReferenced in:4.11.1. The details element IDL attribute must reflect the open content attribute.

<section class="progress window">
  <h1>Copying "Really Achieving Your Childhood Dreams"</h1>
  <details>
  <summary>Copying... <progress max="375505392" value="97543282"></progress> 25%</summary>
  <dl>
    <dt>Transfer rate:</dt> <dd>452KB/s</dd>
    <dt>Local filename:</dt> <dd>/home/rpausch/raycd.m4v</dd>
    <dt>Remote filename:</dt> <dd>/var/www/lectures/raycd.m4v</dd>
    <dt>Duration:</dt> <dd>01:16:27</dd>
    <dt>Color profile:</dt> <dd>SD (6-1-6)</dd>
    <dt>Dimensions:</dt> <dd>320×240</dd>
  </dl>
  </details>
</section>

<details>
  <summary><label for=fn>Name & Extension:</label></summary>
  <p><input type=text id=fn name=fn value="Pillar Magazine.pdf">
  <p><label><input type=checkbox name=ext checked> Hide extension</label>
</details>

<style>
  details > summary { transition: color 1s; color: black; }
  details[open] > summary { color: red; }
</style>
<details>
  <summary>Automated Status: Operational</summary>
  <p>Velocity: 12m/s</p>
  <p>Direction: North</p>
</details>

---

A menu is a currently relevant menu element#currently-relevant-menu-elementReferenced in:4.11.6.1. Facets if it is the child of a currently relevant menu element, or if it is the designated pop-up menu of a button element that is not inert, does not have a hidden attribute, and is not the descendant of an element with a hidden attribute.

---

A menu construct#menu-constructReferenced in:4.11.3. The menu element (2) (3) (4) (5) (6) consists of an ordered list of zero or more menu item constructs#menu-item-constructsReferenced in:4.11.3. The menu element (2) (3) (4), which can be any of:

• Commands, which can be marked as default commands#default-commandsReferenced in:4.11.3. The menu element (menuitem)
• Separators#separatorsReferenced in:4.9.13. Table sorting model (2) (3)4.11.3. The menu element (2) (3) (4) (5) (6) (7) (hr)
• Other menu constructs, each with an associated submenu label#submenu-labelReferenced in:4.11.3. The menu element (2), which allows the list to be nested (menu)

To build and show a menu#build-and-showReferenced in:4.10.6. The button element4.11.5.2. Processing model for a particular menu element source and with a particular element subject as a subject, the user agent must run the following steps:

1. Let pop-up menu be the menu construct created by the build a menu construct algorithm when passed the source element.

2. Display pop-up menu to the user, and let the algorithm that invoked this one continue.

   If the user selects a menu item construct that corresponds to an element that still represents a command when the user selects it, then the user agent must invoke that command’s Action. If the command’s Action is defined as firing a click event, either directly or via the run synthetic click activation steps algorithm, then the relatedTarget attribute of that click event must be initialized to subject.

   Pop-up menus must not, while being shown, reflect changes in the DOM. The menu is constructed from the DOM before being shown, and is then immutable.

To build a menu construct#build-a-menu-constructReferenced in:4.11.3. The menu element (2) for an element source, the user agent must run the following steps, which return a menu construct:

1. Let generated menu be an empty menu construct.

2. Run the menu item generator steps for the menu element using generated menu as the output.

   The menu item generator#menu-item-generatorReferenced in:4.11.3. The menu element (2) steps for a menu element using a specific menu construct output as output are as follows: For each child node of the menu in tree order, run the appropriate steps from the following list:

   If the child is a menuitem element that defines a command

   Append the command to output, respecting the command’s facets. If the menuitem element has a default attribute, mark the command as being a default command.

   If the child is an hr element

   Append a separator to output.

   If the child is a menu element with no label attribute

   Append a separator to output, then run the menu item generator steps for this child menu element, using output as the output, then append another separator to output.

   If the child is a menu element with a label attribute

   Let submenu be the result of running the build a menu construct steps for the child menu element. Then, append submenu to output, using the value of the child menu element’s label attribute as the submenu label.

   Otherwise

   Ignore the child node.

3. Remove from output any menu construct whose submenu label is the empty string.
4. Remove from output any menu item construct representing a command whose Label is the empty string.
5. Collapse all sequences of two or more adjacent separators in output to a single separator.
6. If the first menu item construct in output is a separator, then remove it.
7. If the last menu item construct in output is a separator, then remove it.
8. Return output.

---

The type#dom-htmlmenuelement-typeReferenced in:4.11.3. The menu element IDL attribute must reflect the content attribute of the same name, limited to only known values.

The label#dom-htmlmenuelement-labelReferenced in:4.11.3. The menu element IDL attribute must reflect the content attribute of the same name.

<menu>
  <li>
  <button type=menu value="File" menu="filemenu">
  <menu id="filemenu" type="context">
    <menuitem onclick="fnew()" label="New...">
    <menuitem onclick="fopen()" label="Open...">
    <menuitem onclick="fsave()" label="Save">
    <menuitem onclick="fsaveas()" label="Save as...">
  </menu>
  </li>
  <li>
  <button type=menu value="Edit" menu="editmenu">
  <menu id="editmenu" type="context">
    <menuitem onclick="ecopy()" label="Copy">
    <menuitem onclick="ecut()" label="Cut">
    <menuitem onclick="epaste()" label="Paste">
  </menu>
  </li>
  <li>
  <button type=menu value="Help" menu="helpmenu">
  <menu id="helpmenu" type="context">
    <menuitem onclick="location='help.html'" label="Help">
    <menuitem onclick="location='about.html'" label="About">
  </menu>
  </li>
</menu>

---

The type#dom-htmlmenuitemelement-typeReferenced in:4.11.4. The menuitem element IDL attribute must reflect the content attribute of the same name, limited to only known values.

The label#dom-htmlmenuitemelement-labelReferenced in:4.11.4. The menuitem element, icon#dom-htmlmenuitemelement-iconReferenced in:4.11.4. The menuitem element, disabled#dom-htmlmenuitemelement-disabledReferenced in:4.11.4. The menuitem element, checked#dom-htmlmenuitemelement-checkedReferenced in:4.11.4. The menuitem element, and radiogroup#dom-htmlmenuitemelement-radiogroupReferenced in:4.11.4. The menuitem element, and default#dom-htmlmenuitemelement-defaultReferenced in:4.11.4. The menuitem element IDL attributes must reflect the respective content attributes of the same name.

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If the element’s Disabled State is false (enabled) then the element’s activation behavior depends on the element’s type attribute, as follows:

If the type attribute is in the Checkbox state

If the element has a checked attribute, the user agent must remove that attribute. Otherwise, the user agent must add a checked attribute, with the literal value "checked".

If the type attribute is in the Radio state

If the element has a parent, then the user agent must walk the list of child nodes of that parent element, and for each node that is a menuitem element, if that element has a radiogroup attribute whose value exactly matches the current element’s (treating missing radiogroup attributes as if they were the empty string), and has a checked attribute, must remove that attribute.

Then, the element’s checked attribute must be set to the literal value "checked".

Otherwise

The element’s activation behavior is to do nothing.

Firing a synthetic click event at the element does not cause any of the actions described above to happen.

If the element’s Disabled State is true (disabled) then the element has no activation behavior.

<button type=menu menu=editmenu>Commands...</button>
<menu type="context" id="editmenu">
  <menuitem type="radio" radiogroup="alignment" checked="checked"
          label="Left" icon="icons/alL.png" onclick="setAlign('left')">
  <menuitem type="radio" radiogroup="alignment"
          label="Center" icon="icons/alC.png" onclick="setAlign('center')">
  <menuitem type="radio" radiogroup="alignment"
          label="Right" icon="icons/alR.png" onclick="setAlign('right')">
  <hr>
  <menuitem type="command" disabled
          label="Publish" icon="icons/pub.png" onclick="publish()">
</menu>

<form name="npc">
  <label>Character name: <input name=char type=text contextmenu=namemenu required></label>
  <menu type=context id=namemenu>
  <menuitem label="Pick random name" onclick="document.forms.npc.elements.char.value = getRandomName()">
  <menuitem label="Prefill other fields based on name" onclick="prefillFields(document.forms.npc.elements.char.value)">
  </menu>
</form>

4.11.5.2. Processing model

Each element has an assigned context menu#assigned-context-menuReferenced in:4.11.5.2. Processing model (2) (3) (4) (5) (6) (7), which can be null. If an element A has a contextmenu attribute, and there is an element with the ID given by A’s contextmenu attribute’s value in A’s home subtree, and the first such element in tree order is a menu element whose type attribute is in the popup menu state, then A’s assigned context menu is that element. Otherwise, if A has a parent element, then A’s assigned context menu is the assigned context menu of its parent element. Otherwise, A’s assigned context menu is null.

When an element’s context menu is requested (e.g., by the user right-clicking the element, or pressing a context menu key), the user agent must apply the appropriate rules from the following list:

If the user requested a context menu using a pointing device

The user agent must fire a trusted event with the name contextmenu, that bubbles and is cancelable, and that uses the MouseEvent interface, at the element for which the menu was requested. The context information of the event must be initialized to the same values as the last MouseEvent user interaction event that was fired as part of the gesture that was interpreted as a request for the context menu.

Otherwise

The user agent must fire a synthetic mouse event named contextmenu that bubbles and is cancelable at the element for which the menu was requested.

Typically, therefore, the firing of the contextmenu event will be the default action of a mouseup or keyup event. The exact sequence of events is user agent-dependent, as it will vary based on platform conventions.

The default action of the contextmenu event depends on whether or not the element for which the menu was requested has a non-null assigned context menu when the event dispatch has completed, as follows.

If the assigned context menu of the element for which the menu was requested is null, the default action must be for the user agent to show its default context menu, if it has one.

Otherwise, let subject be the element for which the menu was requested, and let menu be the assigned context menu of target immediately after the contextmenu event’s dispatch has completed. The user agent must fire a trusted event with the name show at menu, using the RelatedEvent interface, with the relatedTarget attribute initialized to subject. The event must be cancelable.

If this event (the show event) is not canceled, then the user agent must build and show the menu for menu with subject as the subject.

The user agent may also provide access to its default context menu, if any, with the context menu shown. For example, it could merge the menu items from the two menus together, or provide the page’s context menu as a submenu of the default menu. In general, user agents are encouraged to de-emphasize their own contextual menu items, so as to give the author’s context menu the appearance of legitimacy — to allow documents to feel like "applications" rather than "mere Web pages".

User agents may provide means for bypassing the context menu processing model, ensuring that the user can always access the user agent’s default context menus. For example, the user agent could handle right-clicks that have the Shift key depressed in such a way that it does not fire the contextmenu event and instead always shows the default context menu.

---

The contextMenu#dom-htmlelement-contextmenuReferenced in:3.2.2. Elements in the DOM IDL attribute must reflect the contextmenu content attribute.

<img src="cats.jpeg" alt="Cats" contextmenu=catsmenu>
<menu type="context" id="catsmenu">
  <menuitem label="Pet the kittens" onclick="kittens.pet()">
  <menuitem label="Cuddle with the kittens" onclick="kittens.cuddle()">
  <menu label="Feed the kittens">
  <menuitem label="Fish" onclick="kittens.feed(fish)">
  <menuitem label="Chicken" onclick="kittens.feed(chicken)">
  </menu>
</menu>

[Constructor(DOMString type, optional RelatedEventInit eventInitDict)]
interface RelatedEvent#relatedevent-relatedeventReferenced in:Events : Event {
  readonly attribute EventTarget? relatedTarget;
};

dictionary RelatedEventInit#dictdef-relatedevent-relatedeventinitReferenced in:4.11.5.3. The RelatedEvent interfaces : EventInit {
  EventTarget? relatedTarget;
};

The relatedTarget#dom-relatedevent-relatedtargetReferenced in:4.11.5.3. The RelatedEvent interfaces attribute must return the value it was initialized to. When the object is created, this attribute must be initialized to null. It represents the other event target that is related to the event.

4.11.6.2. Using the a element to define a command

An a element with an href attribute defines a command.

The Label of the command is the string given by the element’s textContent IDL attribute.

The Access Key of the command is the element’s assigned access key, if any.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State facet of the command is true if the element or one of its ancestors is inert, and false otherwise.

The Action of the command, if the element has a defined activation behavior, is to run synthetic click activation steps on the element. Otherwise, it is just to fire a click event at the element.

4.11.6.3. Using the button element to define a command

A button element always defines a command.

The Label, Access Key, Hidden State, and Action facets of the command are determined as for a elements (see the previous section).

The Disabled State of the command is true if the element or one of its ancestors is inert, or if the element’s disabled state is set, and false otherwise.

4.11.6.4. Using the input element to define a command

An input element whose type attribute is in one of the submit button, reset button, Image Button, Button, Radio Button, or Checkbox states defines a command.

The Label of the command is determined as follows:

• If the type attribute is in one of the submit button, reset button, Image Button, or Button states, then the Label is the string given by the value attribute, if any, and a user agent-dependent, locale-dependent value that the user agent uses to label the button itself if the attribute is absent.
• Otherwise, if the element is a labeled control, then the Label is the string given by the textContent of the first label element in tree order whose labeled control is the element in question. (In DOM terms, this is the string given by element.labels[0].textContent.)
• Otherwise, if the value attribute is present, then the Label is the value of that attribute.
• Otherwise, the Label is the empty string.

The Access Key of the command is the element’s assigned access key, if any.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State of the command is true if the element or one of its ancestors is inert, or if the element’s disabled state is set, and false otherwise.

The Action of the command, if the element has a defined activation behavior, is to run synthetic click activation steps on the element. Otherwise, it is just to fire a click event at the element.

4.11.6.5. Using the option element to define a command#menu-commandReferenced in:4.10.7. The select element (2)

An option element with an ancestor select element and either no value attribute or a value attribute that is not the empty string defines a command.

The Label of the command is the value of the option element’s label attribute, if there is one, or else the value of option element’s textContent IDL attribute, with leading and trailing whitespace stripped, and with any sequences of two or more space characters replaced by a single U+0020 SPACE character.

The Access Key of the command is the element’s assigned access key, if any.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State of the command is true if the element is disabled, or if its nearest ancestor select element is disabled, or if it or one of its ancestors is inert, and false otherwise.

If the option’s nearest ancestor select element has a multiple attribute, the Action of the command is to pick the option element. Otherwise, the Action is to toggle the option element.

4.11.6.6. Using the menuitem element to define a command

A menuitem element always defines a command.

The Label of the command is the value of the element’s label attribute, if there is one, or the empty string if it doesn’t.

The Access Key of the command is the element’s assigned access key, if any.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State of the command is true if the element or one of its ancestors is inert, or if the element has a disabled attribute, and false otherwise.

The Action of the command, if the element has a defined activation behavior, is to run synthetic click activation steps on the element. Otherwise, it is just to fire a click event at the element.

4.11.6.7. Using the accesskey attribute on a label element to define a command

A label element that has an assigned access key and a labeled control and whose labeled control defines a command, itself defines a command.

The Label of the command is the string given by the element’s textContent IDL attribute.

The Access Key of the command is the element’s assigned access key.

The Hidden State, Disabled State, and Action facets of the command are the same as the respective facets of the element’s labeled control.

4.11.6.8. Using the accesskey attribute on a legend element to define a command

A legend element that has an assigned access key and is a child of a fieldset element that has a descendant that is not a descendant of the legend element and is neither a label element nor a legend element but that defines a command, itself defines a command.

The Label of the command is the string given by the element’s textContent IDL attribute.

The Access Key of the command is the element’s assigned access key.

The Hidden State, Disabled State, and Action facets of the command are the same as the respective facets of the first element in tree order that is a descendant of the parent of the legend element that defines a command but is not a descendant of the legend element and is neither a label nor a legend element.

4.11.6.9. Using the accesskey attribute to define a command on other elements

An element that has an assigned access key defines a command.

If one of the earlier sections that define elements that define commands define that this element defines a command, then that section applies to this element, and this section does not. Otherwise, this section applies to that element.

The Label of the command depends on the element. If the element is a labeled control, the textContent of the first label element in tree order whose labeled control is the element in question is the Label (in DOM terms, this is the string given by element.labels[0].textContent). Otherwise, the Label is the textContent of the element itself.

The Access Key of the command is the element’s assigned access key.

The Hidden State of the command is true (hidden) if the element has a hidden attribute, and false otherwise.

The Disabled State of the command is true if the element or one of its ancestors is inert, and false otherwise.

The Action of the command is to run the following steps:

1. Run the focusing steps for the element.
2. If the element has a defined activation behavior, run synthetic click activation steps on the element.
3. Otherwise, if the element does not have a defined activation behavior, fire a click event at the element.

A dialog element without an open attribute specified should not be shown to the user. This requirement may be implemented indirectly through the style layer. For example, user agents that support the suggested default rendering implement this requirement using the CSS rules described in §10 Rendering.

When the show()#dom-htmldialogelement-showReferenced in:4.11.7. The dialog element method is invoked, the user agent must run the following steps:

1. If the element already has an open attribute, then abort these steps.
2. Add an open attribute to the dialog element, whose value is the empty string.
3. If the show() method was invoked with an argument, set up the position of the dialog element, using that argument as the anchor. Otherwise, set the dialog to the normal alignment mode.
4. Run the dialog focusing steps for the dialog element.

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Each Document has a stack of dialog elements known as the pending dialog stack#pending-dialog-stackReferenced in:4.11.7. The dialog element (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14). When a Document is created, this stack must be initialized to be empty.

When an element is added to the pending dialog stack, it must also be added to the top layer. When an element is removed from the pending dialog stack, it must be removed from the top layer. [FULLSCREEN]

When the #modal-dialog-is-shownReferenced in:5.4.4. Processing modelshowModal()#dom-htmldialogelement-showmodalReferenced in:4.11.7. The dialog element method is invoked, the user agent must run the following steps:

1. Let subject be the dialog element on which the method was invoked.
2. If subject already has an open attribute, then throw an InvalidStateError exception and abort these steps.
3. If subject is not in a Document, then throw an InvalidStateError exception and abort these steps.
4. Add an open attribute to subject, whose value is the empty string.
5. If the showModal() method was invoked with an argument, set up the position of subject, using that argument as the anchor. Otherwise, set the dialog to the centered alignment mode.
6. Let subject’s node document be blocked by the modal dialog subject.
7. Push subject onto subject’s node document’s pending dialog stack.
8. Run the dialog focusing steps for subject.

The dialog focusing steps#dialog-focusing-stepsReferenced in:4.11.7. The dialog element (2) for a dialog element subject are as follows:

1. If for some reason subject is not a control group owner at this point, or if it is inert, abort these steps.

2. Let control be the first non-inert focusable area in subject’s control group whose DOM anchor has an autofocus attribute specified.

   If there isn’t one, then let control be the first non-inert focusable area in subject’s control group.

   If there isn’t one of those either, then let control be subject.

3. Run the focusing steps for control.

If at any time a dialog element is removed from a Document, then if that dialog is in that Document’s pending dialog stack, the following steps must be run:

1. Let subject be that dialog element and document be the Document from which it is being removed.
2. Remove subject from document’s pending dialog stack.
3. If document’s pending dialog stack is not empty, then let document be blocked by the modal dialog that is at the top of document’s pending dialog stack. Otherwise, let document be no longer blocked by a modal dialog at all.

When the close()#dom-htmldialogelement-closeReferenced in:4.11.7. The dialog element method is invoked, the user agent must close the dialog that the method was invoked on. If the method was invoked with an argument, that argument must be used as the return value; otherwise, there is no return value.

When a dialog element subject is to be closed#close-the-dialogReferenced in:4.10.22.3. Form submission algorithm4.11.7. The dialog element (2), optionally with a return value result, the user agent must run the following steps:

1. If subject does not have an open attribute, then abort these steps.
2. Remove subject’s open attribute.
3. If the argument result was provided, then set the returnValue attribute to the value of result.

4. If subject is in its Document’s pending dialog stack, then run these substeps:

   1. Remove subject from that pending dialog stack.
   2. If that pending dialog stack is not empty, then let subject’s node document be blocked by the modal dialog that is at the top of the pending dialog stack. Otherwise, let document be no longer blocked by a modal dialog at all.
5. Queue a task to fire a simple event named close at subject.

The returnValue#dom-htmldialogelement-returnvalueReferenced in:4.11.7. The dialog element IDL attribute, on getting, must return the last value to which it was set. On setting, it must be set to the new value. When the element is created, it must be set to the empty string.

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Canceling dialogs: When a Document’s pending dialog stack is not empty, user agents may provide a user interface that, upon activation, queues a task to fire a simple event named cancel that is cancelable at the top dialog element on the Document’s pending dialog stack. The default action of this event must be to check if that element has an open attribute, and if it does, close the dialog with no return value.

An example of such a UI mechanism would be the user pressing the "Escape" key.

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All dialog elements are always in one of three modes: normal alignment#normal-alignmentReferenced in:4.11.7. The dialog element (2) (3), centered alignment#centered-alignmentReferenced in:4.11.7. The dialog element (2) (3) (4) (5) (6) (7), and magic alignment#magically-alignedReferenced in:4.11.7. The dialog element (2) (3). When a dialog element is created, it must be placed in the normal alignment mode. In this mode, normal CSS requirements apply to the element. The centered alignment mode is only used for dialog elements that are in the top layer. [FULLSCREEN] [CSS-2015]

When an element subject is placed in centered alignment mode, and when it is in that mode and has new rendering boxes created, the user agent must set up the element such that its top static position, for the purposes of calculating the used value of the top property, is the value that would place the element’s top margin edge as far from the top of the viewport as the element’s bottom margin edge from the bottom of the viewport, if the element’s height is less than the height of the viewport, and otherwise is the value that would place the element’s top margin edge at the top of the viewport.

If there is a dialog element with centered alignment and that is being rendered when its browsing context changes viewport width (as measured in CSS pixels), then the user agent must recreate the element’s boxes, recalculating its top static position as in the previous paragraph.

This top static position of a dialog element with centered alignment must remain the element’s top static position until its boxes are recreated. (The element’s static position is only used in calculating the used value of the top property in certain situations; it’s not used, for instance, to position the element if its position property is set to static.)

When a user agent is to set up the position#set-up-the-positionReferenced in:4.11.7. The dialog element (2) (3) of an element subject using an anchor anchor, it must run the following steps:

1. If anchor is a MouseEvent object, then run these substeps:

   1. If anchor’s target element does not have a rendered box, or is in a different document than subject, then let subject be in the centered alignment mode, and abort the set up the position steps.
   2. Let anchor element be an anonymous element rendered as a box with zero height and width (so its margin and border boxes both just form a point), positioned so that its top and left are at the coordinate identified by the event, and whose properties all compute to their initial values.

   Otherwise, let anchor element be anchor.

2. Put subject in the magic alignment mode, aligned to anchor element.

While an element A has magic alignment, aligned to an element B, the following requirements apply:

• If at any time either A or B cease having rendered boxes, A and B cease being in the same Document, or B ceases being earlier than A in tree order, then, if subject is in the pending dialog stack, let subject’s mode become centered alignment, otherwise, let subject’s mode become normal alignment.

• A’s position property must compute to the keyword 'absolute-anchored' rather than whatever it would otherwise compute to (i.e., the position property’s specified value is ignored).

  The 'absolute-anchored' keyword’s requirements are described below.

• The anchor points for A and B are defined as per the appropriate entry in the following list:

  If the computed value of anchor-point is none on both A and B

  The anchor points of A and B are the center points of their respective first boxes' border boxes.

  If the computed value of anchor-point is none on A and a specific point on B

  The anchor point of B is the point given by its anchor-point property.

  If the anchor point of B is the center point of B’s first box’s border box, then A’s anchor point is the center point of its first box’s margin box.

  Otherwise, A’s anchor point is on one of its margin edges. Consider four hypothetical half-infinite lines L1, L2, L3, and L4 that each start in the center of B’s first box’s border box, and that extend respectively through the top left corner, top right corner, bottom right corner, and bottom left corner of B’s first box’s border box. A’s anchor point is determined by the location of B’s anchor point relative to these four hypothetical lines, as follows:

  If the anchor point of B lies on L1 or L2, or inside the area bounded by L1 and L2 that also contains the points above B’s first box’s border box, then let A’s anchor point be the horizontal center of A’s bottom margin edge.

  Otherwise, if the anchor point of B lies on L3 or L4, or inside the area bounded by L4 and L4 that also contains the points below B’s first box’s border box, then let A’s anchor point be the horizontal center of A’s top margin edge.

  Otherwise, if the anchor point of B lies inside the area bounded by L4 and L1 that also contains the points to the left of B’s first box’s border box, then let A’s anchor point be the vertical center of A’s right margin edge.

  Otherwise, the anchor point of B lies inside the area bounded by L2 and L3 that also contains the points to the right of B’s first box’s border box; let A’s anchor point be the vertical center of A’s left margin edge.

  If the computed value of anchor-point is a specific point on A and none on B

  The anchor point of A is the point given by its anchor-point property.

  If the anchor point of A is the center point of A’s first box’s margin box, then B’s anchor point is the center point of its first box’s border box.

  Otherwise, B’s anchor point is on one of its border edges. Consider four hypothetical half-infinite lines L1, L2, L3, and L4 that each start in the center of A’s first box’s margin box, and that extend respectively through the top left corner, top right corner, bottom right corner, and bottom left corner of A’s first box’s margin box. B’s anchor point is determined by the location of A’s anchor point relative to these four hypothetical lines, as follows:

  If the anchor point of A lies on L1 or L2, or inside the area bounded by L1 and L2 that also contains the points above A’s first box’s margin box, then let B’s anchor point be the horizontal center of B’s bottom border edge.

  Otherwise, if the anchor point of A lies on L3 or L4, or inside the area bounded by L4 and L4 that also contains the points below A’s first box’s margin box, then let B’s anchor point be the horizontal center of B’s top border edge.

  Otherwise, if the anchor point of A lies inside the area bounded by L4 and L1 that also contains the points to the left of A’s first box’s margin box, then let B’s anchor point be the vertical center of B’s right border edge.

  Otherwise, the anchor point of A lies inside the area bounded by L2 and L3 that also contains the points to the right of A’s first box’s margin box; let B’s anchor point be the vertical center of B’s left border edge.

  If the computed value of anchor-point is a specific point on both A and B

  The anchor points of A and B are the points given by their respective anchor-point properties.

  The rules above generally use A’s margin box, but B’s border box. This is because while A always has a margin box, and using the margin box allows for the dialog to be positioned offset from the box it is annotating, B sometimes does not have a margin box (e.g., if it is a table-cell), or has a margin box whose position may be not entirely clear (e.g., in the face of margin collapsing and clear handling of in-flow blocks).

  In cases where B does not have a border box but its border box is used by the algorithm above, user agents must use its first box’s content area instead. (This is in particular an issue with boxes in tables that have border-collapse set to collapse.)

• When an element’s position property computes to 'absolute-anchored#absolute-anchoredReferenced in:4.11.7. The dialog element (2) (3) (4)', the float property does not apply and must compute to none, the display property must compute to a value as described by the table in the section of CSS 2.1 describing the relationships between display, position, and float, and the element’s box must be positioned using the rules for absolute positioning but with its static position set such that if the box is positioned in its static position, its anchor point is exactly aligned over the anchor point of the element to which it is magically aligned. Elements aligned in this way are absolutely positioned. For the purposes of determining the containing block of other elements, the 'absolute-anchored' keyword must be treated like the absolute keyword.

The trivial example of an element that does not have a rendered box is one whose display property computes to none. However, there are many other cases; e.g., table columns do not have boxes (their properties merely affect other boxes).

If an element to which another element is anchored changes rendering, the anchored element will be repositioned accordingly. (In other words, the requirements above are live, they are not just calculated once per anchored element.)

The 'absolute-anchored' keyword is not a keyword that can be specified in CSS; the position property can only compute to this value if the dialog element is positioned via the APIs described above.

User agents in visual interactive media should allow the user to pan the viewport to access all parts of a dialog element’s border box, even if the element is larger than the viewport and the viewport would otherwise not have a scroll mechanism (e.g., because the viewport’s overflow property is set to hidden).

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The open#dom-htmldialogelement-openReferenced in:4.11.7. The dialog element IDL attribute must reflect the open content attribute.

<dialog>
  <h2>Add to Wallet</h2>
  <main>
  <p>How many gold coins do you want to add to your wallet?</p>
  <p><input name=amt type=number min=0 step=0.01 value=100></p>
  </main>
  <p><small>You add coins at your own risk.</small></p>
  <p><label><input name=round type=checkbox> Only add perfectly round coins </label>
  <p><input type=button onclick="submit()" value="Add Coins"></p>
</dialog>