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rfc:rfc5261

Network Working Group J. Urpalainen Request for Comments: 5261 Nokia Category: Standards Track September 2008

An Extensible Markup Language (XML) Patch Operations Framework Utilizing

                XML Path Language (XPath) Selectors

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 Extensible Markup Language (XML) documents are widely used as
 containers for the exchange and storage of arbitrary data in today's
 systems.  In order to send changes to an XML document, an entire copy
 of the new version must be sent, unless there is a means of
 indicating only the portions that have changed.  This document
 describes an XML patch framework utilizing XML Path language (XPath)
 selectors.  These selector values and updated new data content
 constitute the basis of patch operations described in this document.
 In addition to them, with basic <add>, <replace>, and <remove>
 directives a set of patches can then be applied to update an existing
 XML document.

Table of Contents

 1. Introduction ....................................................3
 2. Conventions .....................................................3
 3. Basic Features and Requirements .................................4
 4. Patch Operations ................................................5
    4.1. Locating the Target of a Patch .............................6
    4.2. Namespace Mangling .........................................6
         4.2.1. Namespaces Used in Selectors ........................7
         4.2.2. Departures from XPath Requirements ..................7
         4.2.3. Namespaces and Added/Changed Content ................8
    4.3. <add> Element .............................................10
         4.3.1. Adding an Element ..................................11
         4.3.2. Adding an Attribute ................................11
         4.3.3. Adding a Prefixed Namespace Declaration ............12
         4.3.4. Adding Node(s) with the 'pos' Attribute ............12
         4.3.5. Adding Multiple Nodes ..............................12
    4.4. <replace> Element .........................................13

Urpalainen Standards Track [Page 1] RFC 5261 Patch Operations September 2008

         4.4.1. Replacing an Element ...............................14
         4.4.2. Replacing an Attribute Value .......................14
         4.4.3. Replacing a Namespace Declaration URI ..............14
         4.4.4. Replacing a Comment Node ...........................14
         4.4.5. Replacing a Processing Instruction Node ............15
         4.4.6. Replacing a Text Node ..............................15
    4.5. <remove> Element ..........................................15
         4.5.1. Removing an Element ................................15
         4.5.2. Removing an Attribute ..............................16
         4.5.3. Removing a Prefixed Namespace Declaration ..........16
         4.5.4. Removing a Comment Node ............................16
         4.5.5. Removing a Processing Instruction Node .............16
         4.5.6. Removing a Text Node ...............................16
 5. Error Handling .................................................17
    5.1. Error Elements ............................................17
 6. Usage of Patch Operations ......................................19
 7. Usage of Selector Values .......................................19
 8. XML Schema Types of Patch Operation Elements ...................19
 9. XML Schema of Patch Operation Errors ...........................21
 10. IANA Considerations ...........................................23
    10.1. URN Sub-Namespace Registration ...........................23
    10.2. application/patch-ops-error+xml MIME Type ................24
    10.3. Patch-Ops-Types XML Schema Registration ..................25
    10.4. Patch-Ops-Error XML Schema Registration ..................25
 11. Security Considerations .......................................26
 12. Acknowledgments ...............................................26
 13. References ....................................................26
    13.1. Normative References .....................................26
    13.2. Informative References ...................................28
 Appendix A.  Informative Examples .................................29
   A.1.  Adding an Element .........................................29
   A.2.  Adding an Attribute .......................................29
   A.3.  Adding a Prefixed Namespace Declaration ...................30
   A.4.  Adding a Comment Node with the 'pos' Attribute ............30
   A.5.  Adding Multiple Nodes .....................................31
   A.6.  Replacing an Element ......................................31
   A.7.  Replacing an Attribute Value ..............................32
   A.8.  Replacing a Namespace Declaration URI .....................32
   A.9.  Replacing a Comment Node ..................................33
   A.10. Replacing a Processing Instruction Node ...................33
   A.11. Replacing a Text Node .....................................34
   A.12. Removing an Element .......................................34
   A.13. Removing an Attribute .....................................35
   A.14. Removing a Prefixed Namespace Declaration .................35
   A.15. Removing a Comment Node ...................................36
   A.16. Removing a Processing Instruction Node ....................36
   A.17. Removing a Text Node ......................................37
   A.18. Several Patches With Namespace Mangling ...................38

Urpalainen Standards Track [Page 2] RFC 5261 Patch Operations September 2008

1. Introduction

 Extensible Markup Language (XML) [W3C.REC-xml-20060816] documents are
 widely used as containers for the exchange and storage of arbitrary
 data in today's systems.  In order to send changes to an XML
 document, an entire copy of the new version must be sent, unless
 there is a means of indicating only the portions that have changed
 (patches).
 This document describes an XML patch framework that utilizes XML Path
 language (XPath) [W3C.REC-xpath-19991116] selectors.  An XPath
 selector is used to pinpoint the specific portion of the XML that is
 the target for the change.  These selector values and updated new
 data content constitute the basis of patch operations described in
 this document.  In addition to them, with basic <add>, <replace>, and
 <remove> directives a set of patches can be applied to update an
 existing target XML document.  With these patch operations, a simple
 semantics for data oriented XML documents
 [W3C.REC-xmlschema-2-20041028] is achieved, that is, modifications
 like additions, removals, or substitutions of elements and attributes
 can easily be performed.  This document does not describe a full XML
 diff format, only basic patch operation elements that can be embedded
 within a full format that typically has additional semantics.
 As one concrete example, in the Session Initiation Protocol (SIP)
 [RFC3903] based presence system a partial PIDF XML document format
 [RFC5262] consists of the existing Presence Information Data Format
 (PIDF) document format combined with the patch operations elements
 described in this document.  In general, patch operations can be used
 in any application that exchanges XML documents, for example, within
 the SIP Events framework [RFC3265].  Yet another example is XCAP-diff
 [SIMPLE-XCAP], which uses this framework for sending partial updates
 of changes to XCAP [RFC4825] resources.

2. Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119, BCP 14
 [RFC2119] and indicate requirement levels for compliant
 implementations.
 The following terms are used in this document:
 Target XML document:  A target XML document that is going to be
    updated with a set of patches.

Urpalainen Standards Track [Page 3] RFC 5261 Patch Operations September 2008

 XML diff document:  An XML document that contains patch operation
    elements, namespace declarations, and all the document content
    changes that are needed in order to transform a target XML
    document into a new patched XML document.
 Patched XML document:  An XML document that results after applying
    one or more patch operations defined in the XML diff document to
    the target XML document.
 Patch operation:  A single change, i.e., a patch that is being
    applied to update a target XML document.
 Patch operation element:  An XML element that represents a single
    patch operation.
 Type definition for an element:  A World Wide Web Consortium (W3C)
    Schema type definition for an element that describes a patch
    operation content.
 In-scope namespace declaration:  A list of all in-scope namespace
    declarations within a context node.  The QName (qualified name)
    expansion of a context node is based on mapping a prefix with one
    of these declarations.  For an element, one namespace binding may
    have an empty prefix.
 Positional constraint:  A number enclosed with square brackets.  It
    can be used as a location step predicate.
 Located target node:  A node that was found from the target XML
    document with the aid of an XPath selector value.
 White space text node:  A text node that contains only white space.

3. Basic Features and Requirements

 In this framework, XPath selector values and new data content are
 embedded within XML elements, the names of which specify the
 modification to be performed: <add>, <replace>, or <remove>.  These
 elements (patch operations) are defined by schema types with the W3C
 Schema language [W3C.REC-xmlschema-1-20041028].  XPath selectors
 pinpoint the target for a change and they are expressed as attributes
 of these elements.  The child node(s) of patch operation elements
 contain the new data content.  In general when applicable, the new
 content SHOULD be moved unaltered to the patched XML document.
 XML documents that are equivalent for the purposes of many
 applications MAY differ in their physical representation.  The aim of
 this document is to describe a deterministic framework where the

Urpalainen Standards Track [Page 4] RFC 5261 Patch Operations September 2008

 canonical form with comments [W3C.REC-xml-c14n-20010315] of an XML
 document determines logical equivalence.  For example, white space
 text nodes MUST be processed properly in order to fulfill this
 requirement as white space is by default significant
 [W3C.REC-xml-c14n-20010315].
 The specifications referencing these element schema types MUST define
 the full XML diff format with an appropriate MIME type [RFC3023] and
 a character set, e.g., UTF-8 [RFC3629].  For example, the partial
 PIDF format [RFC5262] includes this schema and describes additional
 definitions to produce a complete XML diff format for partial
 presence information updates.
 As the schema defined in this document does not declare any target
 namespace, the type definitions inherit the target namespace of the
 including schema.  Therefore, additional namespace declarations
 within the XML diff documents can be avoided.
 It is anticipated that applications using these types will define
 <add>, <replace>, and <remove> elements based on the corresponding
 type definitions in this schema.  In addition, an application may
 reference only a subset of these type definitions.  A future
 extension can introduce other operations, e.g., with
 document-oriented models [W3C.REC-xmlschema-2-20041028], a <move>
 operation and a text node patching algorithm combined with <move>
 would undoubtedly produce smaller XML diff documents.
 The instance document elements based on these schema type definitions
 MUST be well formed and SHOULD be valid.
 The following XPath 1.0 data model node types can be added, replaced,
 or removed with this framework: elements, attributes, namespaces,
 comments, texts, and processing instructions.  The full XML prolog,
 including for example XML entities [W3C.REC-xml-20060816] and the
 root node of an XML document, cannot be patched according to this
 framework.  However, patching of comments and processing instructions
 of the root node is allowed.  Naturally, the removal or addition of a
 document root element is not allowed as any valid XML document MUST
 always contain a single root element.  Also, note that support for
 external entities is beyond the scope of this framework.

4. Patch Operations

 An XML diff document contains a collection of patch operation
 elements, including one or more <add>, <replace>, and <remove>
 elements.  These patch operations will be applied sequentially in the
 document order.  After the first patch has been applied to update a
 target XML document, the patched XML document becomes a new

Urpalainen Standards Track [Page 5] RFC 5261 Patch Operations September 2008

 independent XML document against which the next patch will be
 applied.  This procedure repeats until all patches have successfully
 been processed.

4.1. Locating the Target of a Patch

 Each patch operation element contains a 'sel' attribute.  The value
 of this attribute is an XPath selector with a restricted subset of
 the full XPath 1.0 recommendation.  The 'sel' value is used to locate
 a single unique target node from the target XML document.  This
 located node pinpoints the target for a change and usually it is an
 element, which is for example either updated itself or some child
 node(s) are added into it.  It MAY also be, for instance, a comment
 node, after which some other sibling node(s) are inserted.  In any
 case, it is an error condition if multiple nodes are found during the
 evaluation of this selector value.
 The XPath selections of the 'sel' attribute always start from the
 root node of a document.  Thus, relative location paths SHOULD be
 used so that the starting root node selection "/" can be omitted.
 When locating elements in a document tree, a node test can either be
 a "*" character or a QName [W3C.REC-xml-names-20060816].  A "*"
 character selects all element children of the context node.  Right
 after the node test, a location step can contain one or more
 predicates in any order.  An attribute value comparison is one of the
 most typical predicates.  The string value of the current context
 node or a child element may alternatively be used to identify
 elements in the tree.  The character ".", which denotes a current
 context node selection, is an abbreviated form of "self::node()".
 Lastly, positional constraints like "[2]" can also be used as an
 additional predicate.
 An XPath 1.0 "id()" node-set function MAY also be used to identify
 unique elements from the document tree.  The schema that describes
 the content model of the document MUST then use an attribute with the
 type ID [W3C.REC-xmlschema-2-20041028] or with non-validating XML
 parsers, an "xml:id" [W3C.WD-xml-id-20041109] attribute MUST have
 been used within an instance document.

4.2. Namespace Mangling

 The normal model for namespace prefixes is that they are local in
 scope.  Thus, an XML diff document MAY have different prefixes for
 the namespaces used in the target document.  The agent parsing the
 diff document MUST resolve prefixes separately in both documents in
 order to match the resulting QNames (qualified name) from each.

Urpalainen Standards Track [Page 6] RFC 5261 Patch Operations September 2008

 The XML diff document MUST contain declarations for all namespaces
 used in the diff document.  The diff document declarations are always
 used to determine what namespaces apply within the diff document.

4.2.1. Namespaces Used in Selectors

 A selector in a diff document may use prefixes when naming elements.
 If it does use a prefix, the prefix must be looked up in the diff
 document namespace declarations.
    For example, the patch operation element of a diff document has an
    in-scope namespace declaration "xmlns:a='foo:'" with a selector
    "sel='a:bar'".  The agent processing this patch MUST then look for
    a 'bar' element qualified with the 'foo:' namespace regardless of
    whether the 'foo:' namespace has a prefix assigned in the target
    document or what that prefix is.
 Default namespaces make this model a little more complicated.  When
 the diff document has a default namespace declaration, any element
 selector without a prefix MUST be evaluated using that namespace.
    For example, the patch operation element of a diff document has an
    in-scope namespace declaration "xmlns='foo:'" with a selector
    "sel='bar'".  The agent processing this patch MUST then look for a
    'bar' element qualified with the 'foo:' namespace, regardless of
    whether the 'foo:' namespace has a prefix assigned in the target
    document or what that prefix is.
 Unqualified names are also possible.  If there is no default
 namespace declared, and an element name appears without a prefix,
 then it is an unqualified element name.  If this appears in a
 selector, it MUST match an unqualified element in the target
 document.
    For example, the patch operation element of a diff document has
    only one in-scope namespace declaration "xmlns:a='foo:'" with a
    selector "sel='bar'".  Since the 'bar' element has no prefix, and
    there is no default namespace declaration in scope, the agent
    processing this patch can only match the selector against a 'bar'
    element that has no prefix and also no default namespace in scope.

4.2.2. Departures from XPath Requirements

 The prefix matching rules described previously in this section are
 different from those required in XPath 1.0 and 2.0
 [W3C.REC-xpath20-20070123].  In XPath 1.0, a "bar" selector always
 locates an unqualified <bar> element.  In XPath 2.0, a "bar" selector
 not only matches an unqualified <bar> element, but also matches a

Urpalainen Standards Track [Page 7] RFC 5261 Patch Operations September 2008

 qualified <bar> element that is in scope of a default namespace
 declaration.  In contrast, in this specification, a selector without
 a prefix only matches one element, and it may match an element with
 or without a prefix but only if the namespace it's qualified with (or
 none) is an exact match.
    The XPath 1.0 recommendation specifies "namespace-uri()" and
    "local-name()" node-set functions that can be used within
    predicates.  These functions may be utilized during XPath
    evaluations if there are no other means to "register" prefixes
    with associated namespace URIs.  They can also be used when
    handling selections where default namespaces are attached to
    elements.  However, this specification does not allow the usage of
    these functions.

4.2.3. Namespaces and Added/Changed Content

 Elements within the changed data content are also in scope of
 namespace declarations.  For example, when adding a new namespace
 qualified element to the target XML document, the diff document MUST
 contain a namespace declaration that applies to the element.  The
 agent processing the diff document MUST ensure that the target
 document also contains the same namespace declaration.  Similar to
 XPath, the same namespace declaration in this context means that the
 namespace URIs MUST be equal, but the prefixes MAY be different in
 the diff and target documents.
    For example, if a new added <a:bar> element has a namespace
    declaration reference to "xmlns:a='foo:'" in the diff document and
    the target document has only a single in-scope namespace
    declaration "xmlns:b='foo:'" at the insertion point, the namespace
    reference MUST be changed so that a <b:bar> element will then
    exist in the patched document.  The same rule applies although
    default namespaces were used in either or both of the documents,
    the namespace URIs determine what will be the correct references
    (prefixes) in the patched document.
 When the new or changed content has elements that declare new
 namespaces (locally scoped), these declarations are copied unaltered
 (prefix and everything) from the XML diff document to the target XML
 document.  Default namespace declarations can only be added in this
 way, but prefixed namespace declarations MAY be added or removed with
 XPath namespace axis semantics shown later in this document (look
 Section 4.3.3).
 A fairly difficult use case for these rules is found when the target
 document has several namespace declarations in scope for the same
 namespace.  A target document might declare several different

Urpalainen Standards Track [Page 8] RFC 5261 Patch Operations September 2008

 prefixes for the same namespace.  Normally, the agent applying the
 diff document chooses *the* appropriate prefix for adding new
 elements to the target document, but in this special case there's
 more than one.  These requirements create deterministic behavior for
 this special and in practice rare case:
  1. If the diff document happens to use a prefix that is one of the

prefixes declared for the same namespace in the evaluation context

   node of the target document, this prefix MUST be used in the
   resulting patched document.  An empty evaluable prefix and an
   existing in-scope default namespace declaration means that the
   default namespace MUST be chosen.  In other words, the expanded
   names are then equal within the diff and patched documents.
       In an <add> operation, the evaluation context node is the
       parent element of the inserted node, for example, with a
       selector "sel='*/ bar'" and without a 'pos' attribute directive
       (look Section 4.3), it is the <bar> element of the root
       document element.  With modifications of elements, the
       evaluation context node is the parent element of the modified
       element, and in the previous example thus the root document
       element.
  1. Secondly, the prefix (also empty) of the evaluation context node

MUST be chosen if the namespace URIs are equal.

  1. Lastly, if the above two rules still don't apply, first all

in-scope namespace prefixes of the evaluation context node are

   arranged alphabetically in an ascending order.  If a default
   namespace declaration exists, it is interpreted as the first entry
   in this list.  The prefix from the list is then chosen that appears
   as the closest and just before the compared prefix if it were
   inserted into the list.  If the compared prefix were to exist
   before the first prefix, the first prefix in the list MUST be
   selected (i.e., there's no default namespace).
       For example, if the list of in-scope prefixes in the target
       document is "x", "y" and the compared prefix in the diff
       document is "xx", then the "x" prefix MUST be chosen.  If an
       "a" prefix were evaluated, the "x" prefix, the first entry MUST
       be chosen.  If there were also an in-scope default namespace
       declaration, an evaluable "a" prefix would then select the
       default declaration.  Note that unprefixed attributes don't
       inherit the default namespace declaration.  When adding
       qualified attributes, the default namespace declaration is then
       not on this matching list of prefixes (see Section 4.3.2).

Urpalainen Standards Track [Page 9] RFC 5261 Patch Operations September 2008

 Note that these requirements might mean that a resulting patched
 document could contain unused and/or superfluous namespace
 declarations.  The resulting patched document MUST NOT be "cleaned
 up" such that these namespace declarations are removed.
    Note: In practice, the agent constructing a diff document can
    usually freely select the appropriate prefixes for the namespace
    declarations and it doesn't need to know or care about the actual
    prefixes in the target document unless there are overlapping
    declarations.  In other words, the diff format content is
    typically independent of the target documents usage of namespace
    prefixes.  However, it may be very useful to know where namespaces
    are declared in the target document.  The most typical use case is
    such though, that the agent generating a diff has both the
    previous (target) and new (patched) documents available, and
    namespace declarations are thus exactly known.  Note also, that in
    a case where the target document is not exactly known, it is
    allowed to use locally scoped namespace declarations, the
    consequences of which are larger and less human-readable patched
    documents.

4.3. <add> Element

 The <add> element represents the addition of some new content to the
 target XML document: for example, a new element can be appended into
 an existing element.
 The new data content exists as the child node(s) of the <add>
 element.  When adding attributes and namespaces, the child node of
 the <add> element MUST be a single text node.  Otherwise, the <add>
 element MAY contain any mixture of element, text, comment or
 processing instruction nodes in any order.  All children of the <add>
 element are then copied into a target XML document.  The described
 namespace mangling procedure applies to added elements, which include
 all of their attribute, namespace and descendant nodes.
 The <add> element type has three attributes: 'sel', 'type', and
 'pos'.
 The value of the optional 'type' attribute is only used when adding
 attributes and namespaces.  Then, the located target node MUST be an
 element into which new attributes and namespace declarations are
 inserted.  When the value of this 'type' attribute equals "@attr",
 the string "attr" is the name of the actual attribute being added.
 The value of this new 'attr' attribute is the text node content of
 the <add> element.  The less frequently used prefixed (i.e.,
 namespace-qualified) attributes can also be added.  If the value of
 the 'type' attribute equals "namespace::pref", "pref" is the actual

Urpalainen Standards Track [Page 10] RFC 5261 Patch Operations September 2008

 prefix string to be used for the namespace declaration in the patched
 document and the text node content of the <add> element contains the
 corresponding namespace URI.
    Note: The 'type' attribute is thus also an XPath selector, but it
    only locates attributes and namespaces.  Attribute axis
    "attribute" has an abbreviated form "@" unlike the "namespace"
    axis, which doesn't have an abbreviated form.  Double colons "::"
    are used as an axis separator in XPath.
 The value of the optional 'pos' attribute indicates the positioning
 of new data content.  It is not used when adding attributes or
 namespaces.  When neither 'type' nor 'pos' attribute exist, the
 children of the <add> element are then appended as the last child
 node(s) of the located target element.  When the value of 'pos'
 attribute is "prepend" the new node(s) are added as the first child
 node(s) of the located target element.  With the value of "before",
 the added new node(s) MUST be the immediate preceding sibling
 node(s), and with "after", the immediate following sibling node(s) of
 the located target node.
 Some examples follow that describe the use cases of these <add>
 element attributes.  The nodes are not namespace qualified and
 prefixes are therefore not used, and the whole XML diff content is
 not shown in these examples, only patch operation elements.  Full
 examples are given in an Appendix A.

4.3.1. Adding an Element

 An example for an addition of an element:
 <add sel="doc"><foo id="ert4773">This is a new child</foo></add>
 Once the <doc> element has been found from the target XML document, a
 new <foo> element is appended as the last child node of the <doc>
 element.  The located target node: the <doc> element is naturally the
 root element of the target XML document.  The new <foo> element
 contains an 'id' attribute and a child text node.

4.3.2. Adding an Attribute

 An example for an addition of an attribute:
 <add sel="doc/foo[@id='ert4773']" type="@user">Bob</add>
 This operation adds a new 'user' attribute to the <foo> element that
 was located by using an 'id' attribute value predicate.  The value of
 this new 'user' attribute is "Bob".

Urpalainen Standards Track [Page 11] RFC 5261 Patch Operations September 2008

 A similar patched XML document is achieved when using a validating
 XML parser, if the 'sel' selector value had been 'id("ert4773")' and
 if the data type of the 'id' attribute is "ID"
 [W3C.REC-xmlschema-2-20041028].
 Note that with namespace qualified attributes, the prefix matching
 rules within the 'type' attribute are evaluated with similar rules
 described in Section 4.2.3.  Also, note that then the possible
 default namespace declaration of the context element isn't
 applicable.
    Note: As the 'sel' selector value MAY contain quotation marks,
    escaped forms: "&quot;" or "&apos;" can be used within attribute
    values.  However, it is often more appropriate to use the
    apostrophe (') character as shown in these examples.  An
    alternative is also to interchange the apostrophes and quotation
    marks.

4.3.3. Adding a Prefixed Namespace Declaration

 An example for an addition of a prefixed namespace declaration:
 <add sel="doc" type="namespace::pref">urn:ns:xxx</add>
 This operation adds a new namespace declaration to the <doc> element.
 The prefix of this new namespace node is thus "pref" and the
 namespace URI is "urn:ns:xxx".

4.3.4. Adding Node(s) with the 'pos' Attribute

 An example for an addition of a comment node:
 <add
   sel="doc/foo[@id='ert4773']" pos="before"><!-- comment --></add>
 This operation adds a new comment node just before the <foo> element
 as an immediate preceding sibling node.  This is also an example how
 a 'pos' attribute directive can be used.

4.3.5. Adding Multiple Nodes

 Some complexity arises when so-called white space text nodes exist
 within a target XML document.  The XPath 1.0 data model requires that
 a text node MUST NOT have another text node as an immediate sibling
 node.  For instance, if an add operation is like this:
 <add sel="doc">
   <foo id="ert4773">This is a new child</foo></add>

Urpalainen Standards Track [Page 12] RFC 5261 Patch Operations September 2008

 The <add> element then has two child nodes: a white space text node
 (a linefeed and two spaces) and a <foo> element.  If the existing
 last child of the <doc> element is a text node, its content and the
 white space text node content MUST then be combined together.
 Otherwise, (white space) text nodes can be added just like elements,
 and thus, the canonical form of the patched XML document easily
 remains deterministic.  As several sibling nodes can be inserted with
 a single <add> operation, a "pretty printing" style can easily be
 maintained.
 Still another example about the handling of text nodes.  Consider
 this example:
 <add sel="*/foo/text()[2]" pos="after">new<bar/>elem</add>
 The second text node child of the <foo> element is first located.
 The added new content contains two text nodes and an element.  As
 there cannot be immediate sibling text nodes, the located target text
 node content and the first new text node content MUST be combined
 together.  In essence, if the 'pos' value had been "before", the
 second new text node content would effectively have been prepended to
 the located target text node.
    Note: It is still worth noting that text nodes MAY contain CDATA
    sections, the latter of which are not treated as separate nodes.
    Once these CDATA sections exist within the new text nodes, they
    SHOULD be moved unaltered to the patched XML document.
 While XML entities [W3C.REC-xml-20060816] cannot be patched with this
 framework, the references to other than predefined internal entities
 can exist within text nodes or attributes when the XML prolog
 contains those declarations.  These references may then be preserved
 if both the XML diff and the target XML document have identical
 declarations within their prologs.  Otherwise, references may be
 replaced with identical text as long as the "canonically equivalent"
 rule is obeyed.

4.4. <replace> Element

 The <replace> element represents a replacement operation: for
 example, an existing element is updated with a new element or an
 attribute value is replaced with a new value.  This <replace>
 operation always updates a single node or node content at a time.
 The <replace> element type only has a 'sel' attribute.  If the
 located target node is an element, a comment or a processing
 instruction, then the child of the <replace> element MUST also be of
 the same type.  Otherwise, the <replace> element MUST have text

Urpalainen Standards Track [Page 13] RFC 5261 Patch Operations September 2008

 content or it MAY be empty when replacing an attribute value or a
 text node content.

4.4.1. Replacing an Element

 An example for a replacement of an element:
 <replace sel="doc/foo[@a='1']"><bar a="2"/></replace>
 This will update the <foo> element that has an 'a' attribute with
 value "1".  The located target element is replaced with the <bar>
 element.  So all descendant nodes, namespace declarations, and
 attributes of the replaced <foo> element, if any existed, are thus
 removed.

4.4.2. Replacing an Attribute Value

 An example for a replacement of an attribute value:
 <replace sel="doc/@a">new value</replace>
 This will replace the 'a' attribute content of the <doc> element with
 the value "new value".  If the <replace> element is empty, the 'a'
 attribute MUST then remain in the patched XML document appearing like
 <doc a=""/>.

4.4.3. Replacing a Namespace Declaration URI

 An example for a replacement of a namespace URI:
 <replace sel="doc/namespace::pref">urn:new:xxx</replace>
 This will replace the URI value of 'pref' prefixed namespace node
 with "urn:new:xxx".  The parent node of the namespace declaration
 MUST be the <doc> element, otherwise an error occurs.

4.4.4. Replacing a Comment Node

 An example for a replacement of a comment node:
 <replace sel="doc/comment()[1]"><!-- This is the new content
 --></replace>
 This will replace a comment node.  The located target node is the
 first comment node child of the <doc> element.

Urpalainen Standards Track [Page 14] RFC 5261 Patch Operations September 2008

4.4.5. Replacing a Processing Instruction Node

 An example for a replacement of a processing instruction node:
 <replace sel='doc/processing-instruction("test")'><?test bar="foobar"
 ?></replace>
 This will replace the processing instruction node "test" whose parent
 is the <doc> element.

4.4.6. Replacing a Text Node

 An example for a replacement of a text node:
 <replace
 sel="doc/foo/text()[1]">This is the new text content</replace>
 This will replace the first text node child of the <foo> element.
 The positional constraint "[1]" is not usually needed as the element
 content is rarely of mixed type [W3C.REC-xmlschema-1-20041028] where
 several text node siblings typically exist.
 If a text node is updated and the <replace> element is empty, the
 text node MUST thus be removed as a text node MUST always have at
 least one character of data.

4.5. <remove> Element

 The <remove> element represents a removal operation of, for example,
 an existing element or an attribute.
 The <remove> element type has two attributes: 'sel' and 'ws'.  The
 value of the optional 'ws' attribute is used to remove the possible
 white space text nodes that exist either as immediate following or
 preceding sibling nodes of the located target node.  The usage of
 'ws' attribute is only allowed when removing other types than text,
 attribute and namespace nodes.  If the value of 'ws' is "before", the
 purpose is to remove the immediate preceding sibling node that MUST
 be a white space text node and if the value is "after", the
 corresponding following node.  If the 'ws' value is "both", both the
 preceding and following white space text nodes MUST be removed.

4.5.1. Removing an Element

 An example of a removal of an element including all of its
 descendant, attribute, and namespace nodes:
 <remove sel="doc/foo[@a='1']" ws="after"/>

Urpalainen Standards Track [Page 15] RFC 5261 Patch Operations September 2008

 This will remove the <foo> element as well as the immediate following
 sibling white space text node of the <foo> element.  If the immediate
 following sibling node is not a white space text node, an error
 occurs.

4.5.2. Removing an Attribute

 An example for a removal of an attribute node:
 <remove sel="doc/@a"/>
 This will remove the 'a' attribute node from the <doc> element.

4.5.3. Removing a Prefixed Namespace Declaration

 An example for a removal of a prefixed namespace node:
 <remove sel="doc/foo/namespace::pref"/>
 This will remove the 'pref' prefixed namespace node from the <foo>
 element.  Naturally, this prefix MUST NOT be associated with any node
 prior to the removal of this namespace node.  Also, the parent node
 of this namespace declaration MUST be the <foo> element.

4.5.4. Removing a Comment Node

 An example for a removal of a comment node:
 <remove sel="doc/comment()[1]"/>
 This will remove the first comment node child of the <doc> element.

4.5.5. Removing a Processing Instruction Node

 An example for a removal of a processing instruction node:
 <remove sel='doc/processing-instruction("test")'/>
 This will remove the "test" processing instruction node child of the
 <doc> element.

4.5.6. Removing a Text Node

 An example for a removal of a text node:
 <remove sel="doc/foo/text()[1]"/>
 This will remove the first text node child of the <foo> element.

Urpalainen Standards Track [Page 16] RFC 5261 Patch Operations September 2008

 When removing an element, a comment, or a processing instruction node
 that has immediate preceding and following sibling text nodes without
 the 'ws' directive, the content of these two text nodes MUST be
 combined together.  The latter text node thus disappears from the
 document.

5. Error Handling

 It is an error condition if any of the patch operations cannot be
 unambiguously fulfilled.  In other words, once a particular patch
 operation fails, it is an error condition and processing of further
 patch operations is hardly sensible.
 A new MIME error format is defined for applications that require
 deterministic error handling when patching cannot be applied.  It is
 anticipated that these error elements can be used within other MIME
 types that allow extension elements.

5.1. Error Elements

 The root element of the error document is <patch-ops-error>.  The
 content of this element is a specific error condition.  Each error
 condition is represented by a different element.  This allows for
 different error conditions to provide different data about the nature
 of the error.  All error elements support a "phrase" attribute, which
 can contain text meant for rendering to a human user.  The optional
 "xml:lang" MAY be used to describe the language of the "phrase"
 attribute.  Most of the error condition elements are supposed to
 contain the patch operation element that caused the patch to fail.
 The following error elements are defined by this specification:
 <invalid-attribute-value>:  The validity constraints of 'sel',
    'type', 'ws', or 'pos' attribute values MAY be indicated with this
    error, i.e., non-allowable content has been used.  Also, this
    error can be used to indicate if an added or a modified attribute
    content is not valid, for example, CDATA sections were used when a
    new attribute was intended to be added.
 <invalid-character-set>:  The patch could not be applied because the
    diff and the patched document use different character sets.
 <invalid-diff-format>:  This indicates that the diff body of the
    request was not a well-formed XML document or a valid XML document
    according to its schema.
 <invalid-entity-declaration>:  An entity reference was found but
    corresponding declaration could not be located or resolved.

Urpalainen Standards Track [Page 17] RFC 5261 Patch Operations September 2008

 <invalid-namespace-prefix>:  The namespace URI for the given prefix
    could not be located or resolved, e.g., within the 'sel' attribute
    a prefix was used but its declaration is missing from the target
    document.
 <invalid-namespace-uri>:  The namespace URI value is not valid or the
    target document did not have this declaration.
 <invalid-node-types>:  The node types of a <replace> operation did
    not match, i.e., for example, the 'sel' selector locates an
    element but the replaceable content is of text type.  Also, a
    <replace> operation may locate a unique element, but replaceable
    content had multiple nodes.
 <invalid-patch-directive>:  A patch directive could not be fulfilled
    because the given directives were not understood.
 <invalid-root-element-operation>:  The root element of the document
    cannot be removed or another sibling element for the document root
    element cannot be added.
 <invalid-xml-prolog-operation>:  Patch failure related to XML prolog
    nodes.
 <invalid-whitespace-directive>:  A <remove> operation requires a
    removal of a white space node that doesn't exist in the target
    document.
 <unlocated-node>:  A single unique node (typically an element) could
    not be located with the 'sel' attribute value.  Also, the location
    of multiple nodes can lead to this error.
 <unsupported-id-function>:  The nodeset function id() is not
    supported, and thus attributes with the ID type are not known.
 <unsupported-xml-id>:  The attribute xml:id as an ID attribute in XML
    documents is not supported.
 Additional error elements can be indicated within the root
 <patch-ops-error> element from any namespace.  However, the IETF MAY
 specify additional error elements in the
 "urn:ietf:params:xml:ns:patch-ops-error" namespace.
 As an example, the following document indicates that it was attempted
 to add a new <note> element with white space into a document, but the
 parent element could not be located:

Urpalainen Standards Track [Page 18] RFC 5261 Patch Operations September 2008

 <?xml version="1.0" encoding="UTF-8"?>
 <patch-ops-error
  xmlns:p="urn:ietf:params:xml:ns:pidf-diff"
  xmlns="urn:ietf:params:xml:ns:patch-ops-error">
  <unlocated-node
   phrase="a unique node could not be located with the id() function."
   ><p:add sel='id("ert4773")'>
     <p:note>some text added</p:note>
   </p:add></unlocated-node>
 </patch-ops-error>

6. Usage of Patch Operations

 An XML diff document SHOULD contain only the nodes that have been
 modified as the intention is to try to reduce bandwidth/storage
 requirements.  However, when there's a large collection of changes it
 can be desirable to exchange the full document content instead.  How
 this will be done in practice is beyond the scope of this document.
 Some applications MAY require that the full versioning history MUST
 be indicated although the history had superfluous changes.  This
 framework doesn't mandate any specific behavior, applications MAY
 decide the appropriate semantics themselves.  Also, in practice,
 applications are free to select the proper algorithms when generating
 diff document content.

7. Usage of Selector Values

 It is up to the application to decide what kind of selector values to
 use.  Positional element selectors like "*/*[3]/*[2]" provide the
 shortest selectors, but care must to taken when using them.  When
 there are several removals of sibling elements, the positional
 element indexes change after each update.  Likewise these indexes
 change when new elements are inserted into the tree.  Using names
 with possible attribute predicates like "doc[@sel='foo']" is usually
 easier for an application, be it for example an auto diff tool, but
 it leads to larger diff documents.

8. XML Schema Types of Patch Operation Elements

 The schema types for the patch operation elements.
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE schema [
  <!ENTITY ncname "\i\c*">
  <!ENTITY qname  "(&ncname;:)?&ncname;">
  <!ENTITY aname  "@&qname;">
  <!ENTITY pos    "\[\d+\]">

Urpalainen Standards Track [Page 19] RFC 5261 Patch Operations September 2008

  <!ENTITY attr   "\[&aname;='(.)*'\]|\[&aname;=&quot;(.)*&quot;\]">
  <!ENTITY valueq "\[(&qname;|\.)=&quot;(.)*&quot;\]">
  <!ENTITY value  "\[(&qname;|\.)='(.)*'\]|&valueq;">
  <!ENTITY cond   "&attr;|&value;|&pos;">
  <!ENTITY step   "(&qname;|\*)(&cond;)*">
  <!ENTITY piq    "processing-instruction\((&quot;&ncname;&quot;)\)">
  <!ENTITY pi     "processing-instruction\(('&ncname;')?\)|&piq;">
  <!ENTITY id     "id\(('&ncname;')?\)|id\((&quot;&ncname;&quot;)?\)">
  <!ENTITY com    "comment\(\)">
  <!ENTITY text   "text\(\)">
  <!ENTITY nspa   "namespace::&ncname;">
  <!ENTITY cnodes "(&text;(&pos;)?)|(&com;(&pos;)?)|((&pi;)(&pos;)?)">
  <!ENTITY child  "&cnodes;|&step;">
  <!ENTITY last   "(&child;|&aname;|&nspa;)">
 ]>
 <xsd:schema
      xmlns:xsd="http://www.w3.org/2001/XMLSchema"
      elementFormDefault="qualified">
  <xsd:simpleType name="xpath">
   <xsd:restriction base="xsd:string">
    <xsd:pattern
     value="(/)?((&id;)((/&step;)*(/&last;))?|(&step;/)*(&last;))"/>
   </xsd:restriction>
  </xsd:simpleType>
  <xsd:simpleType name="xpath-add">
   <xsd:restriction base="xsd:string">
    <xsd:pattern
     value="(/)?((&id;)((/&step;)*(/&child;))?|(&step;/)*(&child;))"/>
   </xsd:restriction>
  </xsd:simpleType>
  <xsd:simpleType name="pos">
   <xsd:restriction base="xsd:string">
    <xsd:enumeration value="before"/>
    <xsd:enumeration value="after"/>
    <xsd:enumeration value="prepend"/>
   </xsd:restriction>
  </xsd:simpleType>
  <xsd:simpleType name="type">
   <xsd:restriction base="xsd:string">
    <xsd:pattern value="&aname;|&nspa;"/>
   </xsd:restriction>
  </xsd:simpleType>
  <xsd:complexType name="add">

Urpalainen Standards Track [Page 20] RFC 5261 Patch Operations September 2008

   <xsd:complexContent mixed="true">
    <xsd:restriction base="xsd:anyType">
     <xsd:sequence>
      <xsd:any processContents="lax" namespace="##any"
               minOccurs="0" maxOccurs="unbounded"/>
     </xsd:sequence>
     <xsd:attribute name="sel" type="xpath-add"
                    use="required"/>
     <xsd:attribute name="pos" type="pos"/>
     <xsd:attribute name="type" type="type"/>
    </xsd:restriction>
   </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="replace">
   <xsd:complexContent mixed="true">
    <xsd:restriction base="xsd:anyType">
     <xsd:sequence>
      <xsd:any processContents="lax" namespace="##any"
               minOccurs="0" maxOccurs="1"/>
     </xsd:sequence>
     <xsd:attribute name="sel" type="xpath" use="required"/>
    </xsd:restriction>
   </xsd:complexContent>
  </xsd:complexType>
  <xsd:simpleType name="ws">
   <xsd:restriction base="xsd:string">
    <xsd:enumeration value="before"/>
    <xsd:enumeration value="after"/>
    <xsd:enumeration value="both"/>
   </xsd:restriction>
  </xsd:simpleType>
  <xsd:complexType name="remove">
   <xsd:attribute name="sel" type="xpath" use="required"/>
   <xsd:attribute name="ws" type="ws"/>
  </xsd:complexType>
 </xsd:schema>

9. XML Schema of Patch Operation Errors

 The patch operation errors definitions.
 <?xml version="1.0" encoding="UTF-8"?>
 <xsd:schema
     targetNamespace="urn:ietf:params:xml:ns:patch-ops-error"

Urpalainen Standards Track [Page 21] RFC 5261 Patch Operations September 2008

     xmlns:tns="urn:ietf:params:xml:ns:patch-ops-error"
     xmlns:xsd="http://www.w3.org/2001/XMLSchema"
     elementFormDefault="qualified"
     attributeFormDefault="unqualified">
  <!-- This import brings in the XML language attribute xml:lang-->
  <xsd:import namespace="http://www.w3.org/XML/1998/namespace"
              schemaLocation="http://www.w3.org/2001/xml.xsd"/>
  <!-- ROOT document element for signaling patch-ops errors -->
  <xsd:element name="patch-ops-error">
   <xsd:complexType>
    <xsd:sequence>
     <xsd:any namespace="##any" processContents="lax"
              minOccurs="0" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:anyAttribute processContents="lax"/>
   </xsd:complexType>
  </xsd:element>
  <!-- patch-ops error elements:
       not intended to be used as root documnet elements -->
  <xsd:element name="invalid-attribute-value"
               type="tns:patch-error"/>
  <xsd:element name="invalid-character-set"
               type="tns:patch-error-simple"/>
  <xsd:element name="invalid-diff-format"
               type="tns:patch-error-simple"/>
  <xsd:element name="invalid-entity-declaration"
               type="tns:patch-error"/>
  <xsd:element name="invalid-namespace-prefix"
               type="tns:patch-error"/>
  <xsd:element name="invalid-namespace-uri"
               type="tns:patch-error"/>
  <xsd:element name="invalid-node-types"
               type="tns:patch-error"/>
  <xsd:element name="invalid-patch-directive"
               type="tns:patch-error"/>
  <xsd:element name="invalid-root-element-operation"
               type="tns:patch-error"/>
  <xsd:element name="invalid-xml-prolog-operation"
               type="tns:patch-error"/>
  <xsd:element name="invalid-whitespace-directive"
               type="tns:patch-error"/>
  <xsd:element name="unlocated-node"
               type="tns:patch-error"/>
  <xsd:element name="unsupported-id-function"
               type="tns:patch-error"/>

Urpalainen Standards Track [Page 22] RFC 5261 Patch Operations September 2008

  <xsd:element name="unsupported-xml-id"
               type="tns:patch-error"/>
  <!-- simple patch-ops error type  -->
  <xsd:complexType name="patch-error-simple">
   <xsd:attribute name="phrase" type="xsd:string"/>
   <xsd:attribute ref="xml:lang"/>
   <xsd:anyAttribute processContents="lax"/>
  </xsd:complexType>
  <!-- error type which includes patch operation -->
  <xsd:complexType name="patch-error">
   <xsd:sequence>
    <xsd:any namespace="##any" processContents="lax"/>
   </xsd:sequence>
   <xsd:attribute name="phrase" type="xsd:string"/>
   <xsd:attribute ref="xml:lang"/>
   <xsd:anyAttribute processContents="lax"/>
  </xsd:complexType>
 </xsd:schema>

10. IANA Considerations

 IANA has completed the following actions:
 o  registered a new XML namespace URN according to the procedures of
    RFC 3688 [RFC3688].
 o  registered a new MIME type 'application/patch-ops-error+xml'
    according to the procedures of RFC 4288 [RFC4288] and guidelines
    in RFC 3023 [RFC3023].
 o  registered two XML Schemas according to the procedures of RFC 3688
    [RFC3688].

10.1. URN Sub-Namespace Registration

 This specification registers a new XML namespace, as per the
 guidelines in RFC 3688 [RFC3688].
 URI:  The URI for this namespace is
    urn:ietf:params:xml:ns:patch-ops-error
 Registrant Contact:  IETF, SIMPLE working group, (simple@ietf.org),
    Jari Urpalainen (jari.urpalainen@nokia.com).

Urpalainen Standards Track [Page 23] RFC 5261 Patch Operations September 2008

 XML:
 BEGIN
 <?xml version="1.0"?>
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
   "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
 <head>
   <meta http-equiv="content-type"
      content="text/html;charset=iso-8859-1"/>
   <title>Patch-Ops Error Namespace</title>
 </head>
 <body>
   <h1>Namespace for Patch-Ops Error Documents</h1>
   <h2>urn:ietf:params:xml:ns:patch-ops-error</h2>
   <p>See <a
   href="http://www.rfc-editor.org/rfc/rfc5261.txt">RFC5261</a>.</p>
 </body>
 </html>
 END

10.2. application/patch-ops-error+xml MIME Type

 MIME media type name:  application
 MIME subtype name:  patch-ops-error+xml
 Mandatory parameters:  none
 Optional parameters:  Same as charset parameter application/xml as
    specified in RFC 3023 [RFC3023].
 Encoding considerations:  Same as encoding considerations of
    application/xml as specified in RFC 3023 [RFC3023].
 Security considerations:  See Section 10 of RFC 3023 [RFC3023].
 Interoperability considerations:  none.
 Published specification:  RFC 5261

Urpalainen Standards Track [Page 24] RFC 5261 Patch Operations September 2008

 Applications which use this media type:  This document type has been
    used to support transport of Patch-Ops errors in RFC 5261.
 Additional Information:
    Magic Number:  None
    File Extension:  .xer
    Macintosh file type code:  "TEXT"
    Personal and email address for further information:  Jari
       Urpalainen, jari.urpalainen@nokia.com
    Intended usage:  COMMON
    Author/Change controller:  The IETF

10.3. Patch-Ops-Types XML Schema Registration

 This section registers a new XML Schema, the sole content of which is
 shown in Section 8.
    URI:
    urn:ietf:params:xml:schema:patch-ops
    Registrant Contact:
    IETF, SIMPLE working group, <simple@ietf.org>
    Jari Urpalainen, <jari.urpalainen@nokia.com>

10.4. Patch-Ops-Error XML Schema Registration

 This section registers a new XML Schema, the sole content of which is
 shown in Section 9.
    URI:
    urn:ietf:params:xml:schema:patch-ops-error
    Registrant Contact:
    IETF, SIMPLE working group, <simple@ietf.org>
    Jari Urpalainen, <jari.urpalainen@nokia.com>

Urpalainen Standards Track [Page 25] RFC 5261 Patch Operations September 2008

11. Security Considerations

 Security considerations depend very much on the application that
 utilizes this framework.  Since each application will have different
 needs, threat models, and security features, it will be necessary to
 consider these on an application-by-application basis.
 However, this framework utilizes a limited subset of XPath 1.0.
 Applications may thus be vulnerable to XPath injection attacks that
 can reveal some non-allowable content of an XML document.  Injection
 attacks are most likely with shareable resources where access to a
 resource is limited to only some specific parts for a user, contrary
 to a typical use case of this framework.  To defend against those
 attacks the input MUST be sanitized which can be done, for example,
 by validating the diff formats with these restrictive schemas.

12. Acknowledgments

 The author would like to thank Lisa Dusseault for her efforts
 including BoF arrangements, comments and editing assistance.  The
 author would also like to thank Eva Leppanen, Mikko Lonnfors, Aki
 Niemi, Jonathan Rosenberg, Miguel A. Garcia, Anat Angel, Stephane
 Bortzmeyer, Dave Crocker, Joel Halpern, Jeffrey Hutzelman, David
 Ward, and Chris Newman for their valuable comments and Ted Hardie for
 his input and support.

13. References

13.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [W3C.REC-xml-20060816]
            Maler, E., Paoli, J., Bray, T., Yergeau, F., and C.
            Sperberg-McQueen, "Extensible Markup Language (XML) 1.0
            (Fourth Edition)", World Wide Web Consortium
            Recommendation REC-xml-20060816, August 2006,
            <http://www.w3.org/TR/2006/REC-xml-20060816>.
 [W3C.REC-xpath-19991116]
            DeRose, S. and J. Clark, "XML Path Language (XPath)
            Version 1.0", World Wide Web Consortium Recommendation
            REC-xpath-19991116, November 1999,
            <http://www.w3.org/TR/1999/REC-xpath-19991116>.

Urpalainen Standards Track [Page 26] RFC 5261 Patch Operations September 2008

 [W3C.REC-xml-names-20060816]
            Hollander, D., Bray, T., Layman, A., and R. Tobin,
            "Namespaces in XML 1.0 (Second Edition)", World Wide Web
            Consortium Recommendation REC-xml-names-20060816, August
            2006,
            <http://www.w3.org/TR/2006/REC-xml-names-20060816>.
 [W3C.REC-xmlschema-1-20041028]
            Beech, D., Thompson, H., Maloney, M., and N. Mendelsohn,
            "XML Schema Part 1: Structures Second Edition", World Wide
            Web Consortium Recommendation REC-xmlschema-1-20041028,
            October 2004,
            <http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.
 [W3C.REC-xml-c14n-20010315]
            Boyer, J., "Canonical XML Version 1.0", World Wide Web
            Consortium Recommendation REC-xml-c14n-20010315, March
            2001,
            <http://www.w3.org/TR/2001/REC-xml-c14n-20010315>.
 [W3C.REC-xmlschema-2-20041028]
            Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
            Second Edition", World Wide Web Consortium Recommendation
            REC-xmlschema-2-20041028, October 2004,
            <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.
 [W3C.WD-xml-id-20041109]
            Veillard, D., Walsh, N., and J. Marsh, "xml:id Version
            1.0", W3C LastCall WD-xml-id-20041109, November 2004.
 [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
            10646", STD 63, RFC 3629, November 2003.
 [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
            Types", RFC 3023, January 2001.
 [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
            January 2004.
 [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
            Registration Procedures", BCP 13, RFC 4288, December 2005.

Urpalainen Standards Track [Page 27] RFC 5261 Patch Operations September 2008

13.2. Informative References

 [W3C.REC-xpath20-20070123]
            Berglund, A., Fernandez, M., Chamberlin, D., Boag, S.,
            Robie, J., Kay, M., and J. Simeon, "XML Path Language
            (XPath) 2.0", World Wide Web Consortium Recommendation
            REC-xpath20-20070123, January 2007,
            <http://www.w3.org/TR/2007/REC-xpath20-20070123>.
 [RFC4825]  Rosenberg, J., "The Extensible Markup Language (XML)
            Configuration Access Protocol (XCAP)", RFC 4825, May 2007.
 [RFC3265]  Roach, A., "Session Initiation Protocol (SIP)-Specific
            Event Notification", RFC 3265, June 2002.
 [RFC5262]  Lonnfors, M., Leppanen, E., Khartabil, H., and J.
            Urpalainen, "Presence Information Data format (PIDF)
            Extension for Partial Presence", RFC 5262, September 2008.
 [SIMPLE-XCAP]
            Urpalainen, J. and J. Rosenberg, "An Extensible Markup
            Language (XML) Document Format for Indicating A Change in
            XML Configuration Access Protocol (XCAP) Resources", Work
            in Progress, May 2008.
 [RFC3903]  Niemi, A., Ed., "Session Initiation Protocol (SIP)
            Extension for Event State Publication", RFC 3903, October
            2004.

Urpalainen Standards Track [Page 28] RFC 5261 Patch Operations September 2008

Appendix A. Informative Examples

 All following examples assume an imaginary XML diff document
 including these patch operation elements.

A.1. Adding an Element

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <add sel="doc"><foo id="ert4773">This is a new child</foo></add>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
 <foo id="ert4773">This is a new child</foo></doc>

A.2. Adding an Attribute

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
 <foo id="ert4773">This is a new child</foo></doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <add sel="doc/foo[@id='ert4773']" type="@user">Bob</add>
 </diff>

Urpalainen Standards Track [Page 29] RFC 5261 Patch Operations September 2008

 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
 <foo id="ert4773" user="Bob">This is a new child</foo></doc>

A.3. Adding a Prefixed Namespace Declaration

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
 <foo id="ert4773">This is a new child</foo></doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <add sel="doc" type="namespace::pref">urn:ns:xxx</add>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc xmlns:pref="urn:ns:xxx">
   <note>This is a sample document</note>
 <foo id="ert4773">This is a new child</foo></doc>

A.4. Adding a Comment Node with the 'pos' Attribute

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
 <foo id="ert4773">This is a new child</foo></doc>
 An XML diff document:

<?xml version="1.0" encoding="UTF-8"?> <diff>

<add sel="doc/foo[@id='ert4773']" pos="before"><!-- comment --></add>

</diff>

Urpalainen Standards Track [Page 30] RFC 5261 Patch Operations September 2008

 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
 <!-- comment --><foo id="ert4773">This is a new child</foo></doc>

A.5. Adding Multiple Nodes

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <add sel="doc">
   <foo id="ert4773">This is a new child</foo></add>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <note>This is a sample document</note>
   <foo id="ert4773">This is a new child</foo></doc>

A.6. Replacing an Element

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <replace sel="doc/foo[@a='1']"><bar a="2"/></replace>
 </diff>

Urpalainen Standards Track [Page 31] RFC 5261 Patch Operations September 2008

 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <bar a="2"/>
 </doc>

A.7. Replacing an Attribute Value

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc a="test">
   <foo a="1">This is a sample document</foo>
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <replace sel="doc/@a">new value</replace>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc a="new value">
   <foo a="1">This is a sample document</foo>
 </doc>

A.8. Replacing a Namespace Declaration URI

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc xmlns:pref="urn:test">
   <foo a="1">This is a sample document</foo>
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <replace sel="doc/namespace::pref">urn:new:xxx</replace>
 </diff>

Urpalainen Standards Track [Page 32] RFC 5261 Patch Operations September 2008

 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc xmlns:pref="urn:new:xxx">
   <foo a="1">This is a sample document</foo>
 </doc>

A.9. Replacing a Comment Node

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc xmlns:pref="urn:test">
   <foo a="1">This is a sample document</foo>
   <!-- comment -->
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <replace sel="doc/comment()[1]"><!-- This is the new content
    --></replace>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc xmlns:pref="urn:test">
   <foo a="1">This is a sample document</foo>
   <!-- This is the new content
    -->
 </doc>

A.10. Replacing a Processing Instruction Node

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
   <?test foo="bar"?>
 </doc>

Urpalainen Standards Track [Page 33] RFC 5261 Patch Operations September 2008

 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <replace sel='doc/processing-instruction("test")'
     ><?test bar="foobar"?></replace>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
   <?test bar="foobar"?>
 </doc>

A.11. Replacing a Text Node

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
  <replace sel="doc/foo/text()[1]"
    >This is the new text content</replace></diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is the new text content</foo>
 </doc>

A.12. Removing an Element

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
 </doc>

Urpalainen Standards Track [Page 34] RFC 5261 Patch Operations September 2008

 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
  <remove sel="doc/foo[@a='1']" ws="after"/>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   </doc>

A.13. Removing an Attribute

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc a="foo">
   <foo a="1">This is a sample document</foo>
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
  <remove sel="doc/@a"/>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
 </doc>

A.14. Removing a Prefixed Namespace Declaration

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1" xmlns:pref="urn:test"
    >This is a sample document</foo>
   <!-- comment -->
 </doc>

Urpalainen Standards Track [Page 35] RFC 5261 Patch Operations September 2008

 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <remove sel="doc/foo/namespace::pref"/>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
   <!-- comment -->
 </doc>

A.15. Removing a Comment Node

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
   <!-- comment -->
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <remove sel="doc/comment()[1]" ws="after"/>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
   </doc>

A.16. Removing a Processing Instruction Node

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
   <?test?>
 </doc>

Urpalainen Standards Track [Page 36] RFC 5261 Patch Operations September 2008

 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <remove sel='doc/processing-instruction("test")'/>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
 </doc>

A.17. Removing a Text Node

 An example target XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1">This is a sample document</foo>
 </doc>
 An XML diff document:
 <?xml version="1.0" encoding="UTF-8"?>
 <diff>
   <remove sel="doc/foo/text()[1]"/>
 </diff>
 A result XML document:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc>
   <foo a="1"/>
 </doc>

Urpalainen Standards Track [Page 37] RFC 5261 Patch Operations September 2008

A.18. Several Patches With Namespace Mangling

 An example target XML document where namespace qualified elements
 exist:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc xmlns="urn:ietf:params:xml:ns:xxx"
      xmlns:z="urn:ietf:params:xml:ns:yyy">
   <note>This is a sample document</note>
   <elem a="foo">
     <child/>
   </elem>
   <elem a="bar">
     <z:child/>
   </elem>
 </doc>
 An imaginary XML diff document where prefix "p" corresponds the
 targetNamespace of this imaginary schema:
 <?xml version="1.0" encoding="UTF-8"?>
 <p:diff xmlns="urn:ietf:params:xml:ns:xxx"
         xmlns:y="urn:ietf:params:xml:ns:yyy"
         xmlns:p="urn:ietf:params:xml:ns:diff">
 <p:add sel="doc/elem[@a='foo']">  <!-- This is a new child -->
     <child id="ert4773">
       <y:node/>
     </child>
   </p:add>
 <p:replace sel="doc/note/text()">Patched doc</p:replace>
 <p:remove sel="*/elem[@a='bar']/y:child" ws="both"/>
 <p:add sel="*/elem[@a='bar']" type="@b">new attr</p:add>
 </p:diff>

Urpalainen Standards Track [Page 38] RFC 5261 Patch Operations September 2008

 One possible form of the result XML document after applying the
 patches:
 <?xml version="1.0" encoding="UTF-8"?>
 <doc xmlns="urn:ietf:params:xml:ns:xxx"
      xmlns:z="urn:ietf:params:xml:ns:yyy">
   <note>Patched doc</note>
   <elem a="foo">
     <child/>
     <!-- This is a new child -->
     <child id="ert4773">
       <z:node/>
     </child>
   </elem>
   <elem a="bar" b="new attr"/>
 </doc>
 The <node> and removed <child> element prefixes within the XML diff
 document are different than what are the "identical" namespace
 declarations in the target XML document.  If the target XML document
 had used a prefixed namespace declaration instead of the default one,
 the XML diff document could still have been the same.  The added new
 qualified elements would just have inherited that prefix.

Author's Address

 Jari Urpalainen
 Nokia
 Itamerenkatu 11-13
 Helsinki  00180
 Finland
 Phone: +358 7180 37686
 EMail: jari.urpalainen@nokia.com

Urpalainen Standards Track [Page 39] RFC 5261 Patch Operations September 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Urpalainen Standards Track [Page 40]

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