[XML-SIG] SAX 2.0: Namespaces

[Lars Marius Garshol]

Namespace handling in SAX 2.0
-----------------------------

--- Processing modes:

 - Namespace processing.  In this mode full namespace processing is
   on, and namespace declaration attributes are hidden.  This is
   the default mode, and support for it is required.
 
   http://xml.org/sax/features/namespaces           on
   http://xml.org/sax/features/namespace-prefixes   off
 
 - Namespace processing with prefixes available.  In this mode
   namespace processing is on, and namespace declaration attributes
   are not hidden.  Support for this mode is not required.
 
   http://xml.org/sax/features/namespaces           on
   http://xml.org/sax/features/namespace-prefixes   on
 
 - XML 1.0 processing.  In this mode there is no namespace processing.
   Support for this mode is not required.
 
   http://xml.org/sax/features/namespaces           off
   http://xml.org/sax/features/namespace-prefixes   on


--- Name representation

  (What is set out here goes for both ContentHandler and Attributes.)

  - All element and attribute names consist of a namespace name
    (represented as a (uri, localname) tuple) and a qualified name
    (the raw name, represented by a string). Which parts of this
    information is available depends on the processing mode and the
    parser, but the API provides for all this information.

  - During namespace processing, what namespace declarations are in
    effect at any point in the document can be found from the
    startPrefixMapping/endPrefixMapping events on the ContentHandler
    interface.

  - The namespace name:

    - Required during namespace processing, optional otherwise.

    - If the name is not connected to a namespace, the name tuple
      takes the form (None, localname).

    - Namespace processing is off and the parser is not providing
      namespace names this this value should be the same as the
      qualified name. (Alternatively, it could be None. My mind is not
      made up on this.)

  - The qualified name:

    - Required when namespace-prefixes is on, optional otherwise. That
      is, optional during pure namespace processing mode, required
      with XML 1.0 processing mode and namespace processing with
      prefixes.

    - If the parser does not make qualified names available, the value
      is None. If it does make them available, the value is a string.


--- An example

  <h:hello xmlns:h="http://www.greeting.com/ns/" id="a1"
  h:person="David"/>


  - In namespace processing (without prefixes) mode, the following
  will
    be reported:

    - an element
      - name:  ("http://www.greeting.com/ns/", "hello")
      - qname: "h:hello" or None

    - an attribute
      - name:  (None, "id")
      - qname: "id" or None

    - an attribute
      - name:  ("http://www.greeting.com/ns/", "person")
      - qname: "h:person" or None

  - In namespace processing with prefixes mode, the following will be
    reported:

    - an element
      - name:  ("http://www.greeting.com/ns/", "hello")
      - qname: "h:hello"

    - an attribute
      - name:  (None, "id")
      - qname: "id"

    - an attribute
      - name:  ("http://www.greeting.com/ns/", "person")
      - qname: "h:person"

    - an attribute
      - name:  (None, None) # the attribute cannot be looked up by
      this name...
      - qname: "xmlns:h"

  - In XML 1.0 processing mode, the following will be reported:

    - an element
      - name:  ("http://www.greeting.com/ns/", "hello") or None
      - qname: "h:hello"

    - an attribute
      - name:  (None, "id") or None
      - qname: "id"

    - an attribute
      - name:  ("http://www.greeting.com/ns/", "person") or None
      - qname: "h:person"

    - an attribute
      - name:  (None, None) or None
      - qname: "xmlns:h"