Inclusion as defined in this document is a specific type of [XML Information Set] transformation.
[Definition: The
input for the inclusion transformation consists of a source
infoset.]
[Definition: The output, called the result
infoset, is a new infoset which merges the source infoset
with the infosets of resources identified by URI references or IRI references
appearing in xi:include
elements.] Thus a
mechanism to resolve URIs or IRIs and return the identified resources as
infosets is assumed. Well-formed XML entities that do not have
defined infosets (e.g. an external entity with multiple
top-level elements) are outside the scope of this specification,
either for use as a source
infoset or the result
infoset.
xi:include
elements in the source infoset serve
as inclusion transformation instructions.
[Definition: The
information items located by the xi:include
element
are called the top-level included items
].
[Definition: The
top-level included items
together with their attributes, namespaces, and descendants,
are called the included items
]. The
result infoset is
essentially a copy of the source
infoset, with each xi:include
element
and its descendants replaced by its corresponding
included items.
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 parse="text"
, or it may be unable to access another
part of the document using parse="xml"
and 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.
href
attribute valuesThe value of this attribute is an XML resource identifer 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].
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 should use the accept
and accept-language
attributes
to increase the probability that the resource is provided in the
expected format.
parse="xml"
When parse="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 that described in [XPointer xpointer() Scheme]. An error
in the XPointer is a resource
error.
The [XPointer xpointer() Scheme] is not specified in terms of the [XML Information Set], but instead is based on the [XPath 1.0] Data Model, because the XML Information Set had not yet been developed. The mapping between XPath node locations and information items is straightforward. However, xpointer() assumes that all entities have been expanded. Thus it is a fatal error to attempt to resolve an xpointer() scheme on a document that contains unexpanded entity reference information items.
The set of top-level included items is derived from the acquired infoset as follows.
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.
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.
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.
The inclusion target might be a location set that represents a point. In this case the set of included items is empty.
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.
It is a fatal error for the inclusion target to be an attribute node or a namespace node.
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 parse="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 parse="xml"
.
An xi:include
element pointing to any include
element or ancestor thereof which has already been processed
at a higher level.
parse="text"
When parse="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.
XInclude processors must perform fallback behavior in the event of a resource error, as follows:
If the children of the
xi:include
element information item in the
source infoset contain
exactly one xi:fallback
element, the
top-level included items
consist of the information items corresponding to the result of performing
XInclude processing on the children
of the xi:fallback
element. It is a
fatal error if there is zero or more than
one xi:fallback
element.
Note:
Fallback content is not dependent on the value of the
parse
attribute. The xi:fallback
element can contain markup even when parse="text"
.
Likewise, it can contain a simple string when parse="xml"
.
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="xmlns(xi=http://www.w3.org/2001/XInclude)xpointer(x/xi:include[1])" parse="xml"/> </x>
An XInclude processor may, at
user option, suppress xml:base
and/or xml:lang
fixup.
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.
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 4.5.1 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.
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.
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.
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.
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.
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.