4.1 The Include Location
The value of the href attribute, after escaping
according to 4.1.1 Escaping of href attribute values, is interpreted as either a
URI reference or an IRI reference.
The base URI for relative URIs or IRIs is the base URI of the xi:include
element as specified in [XML Base].
[Definition: The
URI or IRI resulting from resolution of the normalized value of the
href attribute (or the empty string if no attribute appears)
to absolute URI or IRI form is called the include location.]
The absence of a value for the href attribute, either
by the appearance of href="" or by the absence of the
href attribute, represents a case which may be incompatible
with certain implementation strategies. For instance, an XInclude
processor might not have a textual representation of the
source infoset to include
as text, or it may be unable to access another
part of the document when
parsing as XML and using an xpointer because of streamability concerns.
An implementation
may choose to treat any or all
absences of a value for the href attribute as
resource errors.
Implementations should document
the conditions under which such resource
errors occur.
4.1.1 Escaping of href attribute values
The value of this attribute is an XML resource identifier as
defined in [XML 1.1] section 4.2.2 "External Entities", which
is interpreted as [Definition: an IRI Reference as defined in RFC 3987 [IETF RFC 3987]],
after the escaping procedure described in [XML 1.1] section
4.2.2 is applied. If necessary for the implementation, the value may be
further converted to a URI reference as described in [XML 1.1].
4.1.2 Using XInclude with Content Negotiation
The use of a mechanism like HTTP [IETF RFC 2616] content
negotiation introduces an additional level of potential complexity
into the use of XInclude. Developers who use XInclude in situations
where content negotiation is likely or possible should be aware of
the possibility that they will be including content that may differ
structurally from the content they expected, even if that content
is XML. For example, a single URI or IRI may variously return a raw XML
representation of the resource, an XSL-FO [XSL-FO]
representation, or an XHTML [XHTML] representation,
as well as versions in different character encodings or languages.
Authors whose XInclude processing depends on the receipt of
a particular vocabulary of XML can use the accept
and accept-language attributes
to increase the probability that the resource is provided in the
expected format.
4.2 Included Items when processing XML
When processing XML, the
include location is
dereferenced, the resource is fetched, and an infoset is created by
parsing the resource as if the media type were application/xml
(including character encoding determination).
Note:
The specifics of how an infoset is created are intentionally
unspecified, to allow for flexibility by implementations and to
avoid defining a particular processing model for components of
the XML architecture. Particulars of whether DTD or XML schema
validation are performed, for example, are not constrained by
this specification.
Note:
The character encodings of the including and included
resources can be different. This does not affect the resulting
infoset, but might need to be taken into account during any
subsequent serialization.
Resources that are unavailable for any reason (for example the
resource doesn't exist, connection difficulties or security
restrictions prevent it from being fetched, the URI scheme isn't
a fetchable one, the resource is in an unsupported encoding, or the
resource is determined through implementation-specific mechanisms
not to be XML)
result in a resource error.
Resources that contain non-well-formed XML result in a
fatal error.
Note:
The distinction between a resource error and a fatal error
is somewhat implementation-dependent. Consider an include
location returning an HTML document, perhaps as an error page.
One processor might determine that no infoset can be created
from the resource (by examining the media type, for example)
and raise a resource error, enabling fallback behavior.
Another processor with no such heuristics might attempt to
parse the non-XML resource as XML and encounter a
well-formedness (fatal) error.
[Definition:
xi:include elements in this infoset are recursively
processed to create the acquired infoset.
For an intra-document reference (via xpointer attribute)
the source infoset is
used as the acquired infoset.]
[Definition: The portion
of the acquired infoset to be
included is called the inclusion target.] The
document information item of the
acquired infoset serves
as the inclusion target
unless the xpointer attribute is present and identifies a
subresource. XPointers of the forms described in [XPointer Framework]
and [XPointer element() scheme] must
be supported. XInclude processors optionally support other forms of
XPointer such as
those in the
XPointer
Registry. An error
in the XPointer is a resource
error.
The set of top-level
included items is derived from the
acquired infoset as
follows.
4.2.1 Document Information Items
The inclusion target
might be a document information item
(for instance, no specified xpointer attribute, or an
XPointer specifically locating the document root.) In this case,
the set of top-level
included items is the children
of the acquired infoset's
document information item, except for the
document type declaration information item
child, if one exists.
Note:
The XML Information Set specification does not provide for
preservation of white space outside the document element.
XInclude makes no further provision to preserve this white
space.
4.2.2 Multiple Nodes
The inclusion target
might consist of more than a single node. In this case the set of
top-level included
items is the set of information items from the
acquired infoset
corresponding to the nodes referred to by the XPointer, in the order
in which they appear in the acquired infoset.
4.2.3 Range Locations
The inclusion target might
be a location set that represents a range or a set of ranges.
Each range corresponds to a set of information items in the
acquired infoset.
[Definition: An information item is
said to be selected by a range if it occurs after
(in document order) the starting point of the range and before
the ending point of the range.]
[Definition: An
information item is said to be partially selected by
a range if it contains only the starting point of the range, or
only the ending point of the range.] By definition, a
character information item cannot be
partially selected.
The set of top-level
included items is the union, in document order with
duplicates removed, of the information items either
selected or
partially selected
by the range. The children
property of selected
information items is not modified. The
children property of
partially selected
information items is the set of information items that are in
turn either selected or
partially selected,
and so on.
4.2.5 Element, Comment, and Processing Instruction Information Items
The inclusion target
might be an element node, a comment node, or a processing instruction
node, respectively representing an element
information item, a comment information
item, or a processing instruction information
item. In this case the set of
top-level included items
consists of the information item corresponding to the element, comment, or
processing instruction node in the acquired
infoset.
4.2.6 Attribute and Namespace Declaration Information Items
It is a fatal error for the
inclusion target to be an
attribute node or a namespace node.
4.2.7 Inclusion Loops
When recursively processing an xi:include
element, it is a fatal error to process
another xi:include element with an
include location and
xpointer attribute value that have already been processed in the
inclusion chain.
In other words, the following are all legal:
An xi:include element
may reference the document
containing the include element, when processing text.
An xi:include element
may identify a different
part of the same local resource (same href,
different xpointer).
Two non-nested xi:include elements
may identify a resource which
itself contains an xi:include element.
The following are illegal:
An xi:include element pointing to itself or any
ancestor thereof, when processing XML.
An xi:include element pointing to any include
element or ancestor thereof which has already been processed
at a higher level.
4.3 Attribute Copying when processing XML
XInclude can introduce validity errors into a document. In
particular, if a resource containing element information items is
included more than once, and if any of those element information items
have attributes of type ID, then the
result infoset will contain multiple
IDs with the same value.
Some applications will want to attempt to resolve these sorts of
errors and different applications will want to do so in different
ways. In order to facilitate this kind of processing, XInclude 1.1
introduces a new feature: attribute copying.
The effect of attribute copying depends on the namespace
of the attribute on the xi:include element.
If the attribute is not in a namespace or is in the xml:
namespace, it is ignored by attribute copying.
If the attribute is in the http://www.w3.org/2001/XInclude/local-attributes namespace, it
is copied without its namespace onto every
top-level included item that is an element
information item. In other words an attribute with the local name
foo and the namespace name http://www.w3.org/2001/XInclude/local-attributes
on the xi:include element will be copied as an attribute
with the local name foo in no namespace.
Any other attributes
that appear on the
xi:include element will be copied onto every
top-level included item that is an element
information item.
In all cases when an attribute is copied, if the element
information item already has an attribute with the same
name, its value is changed to the value specified on the
xi:include element.
What this means in practice is that an author can use namespace
qualified attributes on the xi:include elements to pass
information through to the XIncluded document. Subsequent processing
on the XIncluded document can use this information to repair any
errors introduced. For example, an attribute could be used to indicate
how duplicate IDs are to be repaired.
Also, while attributes in xml: namespace
are not copied, it is possible to use the set-xml-id
attribute to change xml:id attributes on XIncluded
elements.
4.4 Included Items when processing text
When processing text, the include
location is dereferenced and the resource is fetched
and transformed to a set of character information items. This
feature facilitates the inclusion of working XML examples, as
well as other text-based formats.
Resources that are unavailable for any reason (for example
the resource doesn't exist, connection difficulties or security
restrictions prevent it from being fetched, the URI scheme isn't
a fetchable one, or the resource is in an unsupported encoding) result in a
resource error.
The encoding of such a resource is determined by:
external encoding information, if available, otherwise
if the media type of the resource indicates,
according to XML Media Types [IETF RFC 3023], that the
resource is XML, for example text/xml or
application/xml or matches
text/*+xml or application/*+xml, then the
encoding is determined as specified in [XML 1.0] or
[XML 1.1] section 4.3.3, as appropriate, otherwise
the value of the encoding attribute if one
exists, otherwise
UTF-8.
Byte sequences outside the range allowed by the encoding are a
fatal error. Characters that are not
permitted in XML documents also are a
fatal error.
Each character obtained from the transformation of the resource is
represented in the top-level
included items as a character
information item with the
character code set to the
character code in ISO 10646 encoding, and
the element content whitespace set
to false.
When the first character is U+FEFF and is interpreted as a
Byte-Order Mark, it should be discarded. It is interpreted as a BOM in UTF-8,
UTF-16, and UTF-32 encodings; it is not interpreted as a BOM in the UTF-16LE,
UTF-16BE, UTF-32LE, and UTF-32BE encodings.
The [Character Model] discusses normalization of included text.
4.7 Creating the Result Infoset
The result infoset is a copy of the source infoset,
with each xi:include element processed as follows:
The information item for the xi:include element is
found. [Definition: The
parent property of this item
refers to an information item called the include parent.]
The children property of the
include parent
is modified by replacing the xi:include element
information item with the top-level
included items. The parent
property of each included item is set to the
include parent.
It is a fatal error to attempt to replace an xi:include
element appearing as the document (top-level) element in the source
infoset with something other than a list of zero or more comments,
zero or more processing instructions, and one element.
Some processors may not be able to represent an element's
in-scope namespaces property if
it does not include bindings for all the prefixes bound in its
parent's in-scope namespaces.
Such processors may therefore include
additional namespace bindings inherited from the
include parent in the
in-scope namespaces of
the included items.
The inclusion history of each top-level
included item is recorded in the extension property
include history. The
include history property is
a list of element information items,
representing the xi:include elements for recursive levels
of inclusion. If an include history
property already appears on a top-level
included item, the xi:include element information
item is prepended to the list. If no include
history property exists, then this property is added with the
single value of the xi:include element information item.
The included items will all
appear in the result infoset. This includes unexpanded
entity reference information items if they are present.
Intra-document references within xi:include elements
are resolved against the source infoset. The effect of this is that
the order in which xi:include elements are processed
does not affect the result.
In the following example, the second include always points to
the first xi:include element and not to itself,
regardless of the order in which the includes are processed. Thus
the result of this inclusion is two copies of something.xml,
and does not produce an inclusion loop error.
<x xmlns:xi="http://www.w3.org/2001/XInclude">
<xi:include href="something.xml"/>
<xi:include xpointer="element(x/1)"
parse="application/xml"/>
</x>An XInclude processor may, at
user option, suppress xml:base and/or xml:lang fixup.
4.7.1 Unparsed Entities
Any unparsed entity information
item appearing in the references
property of an attribute on the included
items or any descendant thereof is added to the
unparsed entities
property of the result infoset's
document information item, if
it is not a duplicate of an existing member. Duplicates do not appear
in the result infoset.
Unparsed entity items with the same
name,
system identifier,
public identifier,
declaration base URI,
notation name, and
notation are
considered to be duplicate. An application
may also be able to detect that
unparsed entities are duplicate through other means. For instance,
the URI resulting from combining the system identifier
and the declaration base URI is the same.
It is a fatal error to
include unparsed entity items with the same name, but which are not
determined to be duplicates.
4.7.2 Notations
Any notation information item
appearing in the references
property of an attribute in the included
items or any descendant thereof is added to the
notations property of the
result infoset's
document information item, if
it is not a duplicate of an existing member. Likewise,
any notation referenced by an unparsed entity added as described
in 4.7.1 Unparsed Entities, is added unless it is
a duplicate. Duplicates do not appear in the result infoset.
Notation items with the same
name,
system identifier,
public identifier, and
declaration base URI are
considered to be duplicate. An application may
also be able to detect that notations are duplicate through other means. For
instance, the URI resulting from combining the system identifier
and the declaration base URI is the same.
It is a fatal error to
include notation items with the same name, but which are not
determined to be duplicates.
4.7.3
references Property Fixup
During inclusion, an attribute information
item whose attribute type
property is IDREF or IDREFS has a references
property with zero or more element values from the source or included
infosets. These values must be
adjusted to correspond to element values that occur in the result
infoset. During this process, XInclude also corrects inconsistencies
between the references
property and the attribute type
property, which might arise in the following circumstances:
A document fragment contains an IDREF pointing to an element
in the included document but outside the part being included.
In this case there is no element in the result infoset that
corresponds to the element value in the original
references property.
A document or document fragment is not self-contained.
That is, it contains IDREFs which do not refer to an element within
that document or document fragment, with the intention that these
references will be realized after inclusion. In this case,
the value of the references
property is unknown or has no value.
The result infoset has ID clashes - that is, more than one
attribute with attribute type
ID with the same normalized value.
In this case, attributes with attribute
type IDREF or IDREFS with the same
normalized value might have different values for their
references properties.
In resolving these inconsistencies, XInclude takes the
attribute type property as
definitive. In the result infoset, the value of the
references property of an
attribute information item
whose attribute type property
is IDREF or IDREFS is adjusted as follows:
For each token in the normalized
value property, the references
property contains an element information
item with the same properties as the
element information item in the result
infoset with an attribute with attribute
type ID and normalized
value equal to the token. The order of the elements in
the references property is
the same as the order of the tokens appearing in the
normalize value. If for any of the
token values, no element or more than one element is found, the
references property has no value.
4.7.4 Namespace Fixup
The in-scope namespaces
property ensures that namespace scope is preserved through inclusion.
However, after inclusion, the namespace
attributes property might not provide the full list of
namespace declarations necessary to interpret qualified names in
attribute or element content in the result. It is therefore not
recommended that XInclude processors expose
namespace attributes in the
result. If this is unavoidable, the implementation
may add
attribute information items to the
namespace attributes property
in order to approximate the information conveyed by
in-scope namespaces.
4.7.5 Base URI Fixup
The base URI property of the acquired infoset is not changed as
a result of merging the infoset, and remains unchanged after merging.
Thus relative URI references in the included infoset resolve to the same
URI despite being included into a document with a potentially
different base URI in effect. xml:base attributes are added
to the result infoset to indicate this fact.
Each element information item in
the top-level included
items which has a different base
URI than its include parent
has an attribute information item added to its
attributes property. This attribute has the following properties:
A namespace name of
http://www.w3.org/XML/1998/namespace.
A local name of
base.
A prefix of
xml.
A normalized value
equal to either the base
URI of the element, or an equivalent URI reference
relative to the base URI
of the include parent. The circumstances in which a relative
URI is desirable, and how to compute such a relative URI,
are implementation-dependent.
A specified flag
indicating that this attribute was actually specified in the
start-tag of its element.
An attribute type of
CDATA.
A references property
with no value.
An owner element of the
information item of the element.
If an xml:base attribute information item is already
present, it is replaced by the new attribute.
4.7.6 Language Fixup
While the xml:lang attribute is described as inherited
by XML, the XML Information Set makes no provision for preserving the
inheritance of this property through document composition such as XInclude
provides. This section introduces a language
property which records the scope of xml:lang information in
order to preserve it during inclusion.
An XInclude processor should augment
the source infoset and the
acquired infoset by adding
the language property to each
element information item. The value of
this property is the normalized value
of the xml:lang attribute appearing on that element if one
exists, with xml:lang="" resulting in no value, otherwise it
is the value of the language property
of the element's parent element if one exists, otherwise the property
has no value.
Each element information item in the
top-level included items
which has a different value of language
than its include parent (taking
case-insensitivity into account per [IETF RFC 3066]), or that has
a value if its include parent is
a document information item, has an
attribute information item added to its
attributes property. This attribute
has the following properties:
A namespace name of
http://www.w3.org/XML/1998/namespace.
A local name of
lang.
A prefix of xml.
A normalized value equal to
the language property of the
element. If the language property
has no value, the normalized value is the empty string.
A specified flag indicating
that this attribute was actually specified in the start-tag of its
element.
An attribute type of
CDATA.
A references property with
no value.
An owner element of the
information item of the element.
If an xml:lang attribute information item is already present,
it is replaced by the new attribute.
Note:
The xml:space attribute is not treated specially by
XInclude.
4.7.7 Properties Preserved by the Infoset
As an infoset transformation, XInclude operates on the logical
structure of XML documents, not on their text serialization. All
properties of an information item described in [XML Information Set]
other than those specifically modified by this specification are
preserved during inclusion. The include history
and language
properties introduced in this specification is also preserved.
Extension properties such as
[XML Schemas] Post Schema Validation Infoset (PSVI)
properties are discarded by default. However, an XInclude
processor may, at user option,
preserve these properties in the resulting infoset if they
are correct according to the specification describing the
semantics of the extension properties.
For instance, the PSVI validity
property describes the conditions of ancestors and descendants.
Modification of ancestors and descendants during the XInclude
process can render the value of this property inaccurate. By
default, XInclude strips this property, but by user option the
property could be recalculated to obtain a semantically accurate
value. Precisely how this is accomplished is outside the scope
of this specification.