&abstract; The use of this scheme in a pointer part allows for successful interpretation of element and attribute names used in pointer parts to the right when those names use namespace prefixes.

The key words must, must not, required, shall, shall not, should, should not, recommended, may, and optional in this specification are to be interpreted as described in .

The terms pointer, pointer part, scheme, XPointer processor, application, error, failure, and namespace binding context are used in this specification as defined in the XPointer Framework specification. Note that errors defined by this specification are distinct from XPointer Framework errors.

The formal grammar for the &scheme-phrase; is given using simple Extended Backus-Naur Form (EBNF) notation, as described in the XML Recommendation .

This specification normatively depends on the XPointer Framework specification.

Conforming XPointer processors claiming to support the &scheme-phrase; must conform to the behavior defined in this specification and may conform to additional XPointer scheme specifications.

This section describes the syntax and semantics of the &scheme-phrase; and the behavior of XPointer processors with respect to this scheme.

The scheme name is &schemename;. The scheme data syntax is as follows; if scheme data in a pointer part with the &scheme-phrase; does not conform to the syntax defined in this section, it is an &scheme-phrase; error and the pointer part fails.

S is as defined in the XML specification , and NCName is as defined in the XML Namespaces specification .

A pointer part with the &scheme-phrase; declares a namespace prefix (NCName) to be associated with an XML namespace (NsURIRef). Each pointer part that uses the &scheme-phrase; contributes a new entry to the namespace binding context, and serves to allow successful interpretation of element and attribute names used in pointer parts to the right when those names use namespace prefixes. If a pointer part defines a binding for a namespace prefix that already has an entry in the namespace binding context, the new entry overrides the old one.

For example, the following pointer part binds the abc prefix to the http://example.com/ns/abc namespace name:

A pointer part that uses the &scheme-phrase; never identifies a subresource and thus always fails. However, its evaluation has a potential effect on pointer parts to its right.

If the pointer part fails due to failure to conform to the syntax described in this specification, it does not contribute an entry to the namespace binding context.

The XPointer Framework on which this specification is based dictates that the initial namespace binding context prior to evaluation of the first pointer part consists of a single entry: the xml prefix bound to the URI http:/www.w3.org/XML/1998/namespace. Following the rules specified by the Framework, any attempt by a pointer part using the &scheme-phrase; to redefine the xml prefix will result in no change to the namespace binding context.

The prefixes used in pointer parts need not match the prefixes actually used in the XML resource into which the pointer part is addressing. As an example, assume the following target XML resource:

Evaluation of a pointer part that refers to element x:a will fail if the namespace binding context contains no entry that binds x to a namespace name. The following two pointer parts allow pointer parts to the right to refer to both the outer a element (as x:a) and the inner element (as y:a):