Namespaces in SimpleTaglib

[Ken Neighbors]

I have updated XSP::SimpleTaglib to allow arbitrary namespaces to be
specified for the generated nodes.  A description of this extension to
SimpleTaglib's perl attribute interface is below.

I am seeking feedback on this interface and information on where to
submit the patch if it is deemed useful or if someone wants to try it
out.  (Being new to AxKit there is a slightly nagging question in my
mind that maybe this namespace patch is unnecessary because I may have
missed something.)

Ken Neighbors

XML NAMESPACES in SimpleTaglib

By default, all output elements nodes are placed in the same namespace
as the tag library.  To specify a different namespace or no namespace,
the following shorthand can be used in place of C<name> when
specifying a node name in a result attribute:

  prefix:name:namespaceURI

For example, to create an XML node named C<otherNS:name> and associate
the prefix 'otherNS' with the namespace 'http://mydomain/NS/other/v1':

  node(otherNS:name:http://mydomain/NS/other/v1)

To create an XML node with no namespace, use an empty prefix and an
empty namespace:

  node(:name:)

The shorthand notation for specifying namespaces can also be used in
the C<struct> result attribute.  Alternatively, the standard 'xmlns'
XML attribute may be used to specify namespaces.  For example, the
following are equivalent:

  sub sample_struct : struct {
    return "{ 'otherNS:name:http://mydomain/NS/other/v1' => 'value' }";
  }

  sub sample_struct : struct {
    return q{{
        'otherNS:name' =>
        { '@xmlns:otherNS' => 'http://mydomain/NS/other/v1',
          '' => 'value' }
    }};
  }

Namespace scoping in the hashref is patterned after XML documents.
You may refer to previously declared namespaces by using the same
prefix, and you may override previously declared namespaces with new
declarations (either with shorthand notation or 'xmlns' XML
attributes).

To specify a default prefix and namespace for all unqualified node
names in the hashref, state them as parameters to the C<struct> result
attribute:

  struct(prefix,namespace)

For example, the following is equivalent to the previous example:

  sub sample_struct : struct(otherNS,http://mydomain/NS/other/v1) {
    return "{ 'name' => 'value' }";
  }

To turn off the default namespace for all node names, use empty
parameters for the C<struct> result attribute:

  sub sample_struct : struct("","") {
    return "{ 'name' => 'value' }";
  }

By default, XML attributes created with the C<nodeAttr> output
attribute are not in a namespace.  The shorthand notation can be used
to specify a namespace.  For example:

  nodeAttr(html:href:http://www.w3.org/TR/REC-html40,'http://www.axkit.org/')

If you are specifying more than one attribute in the same namespace,
you can refer to previously declared namespaces by using the same
prefix:

  
nodeAttr(html:href:http://www.w3.org/TR/REC-html40,'http://www.axkit.org/',html:class,'link')

OTHER IDEAS THAT I ABANDONED:

1) create a separate set of result attributes with a 'NS' suffix:

  nodeNS(name,prefix,namespace)
  nodelistNS(name,prefix,namespace)
  exprOrNodeNS(name,prefix,namespace,attrname,attrvalue)
  exprOrNodelistNS(name,prefix,namespace,attrname,attrvalue)
  nodeAttrNS(name,prefix,namespace,expr,...)
  structNS(prefix,namespace)

2) use existing result attributes and include the prefix with the name:

  node(prefix:name,namespace)
  nodelist(prefix:name,namespace)
  exprOrNode(prefix:name,namespace,attrname,attrvalue)
  exprOrNodelist(prefix:name,namespace,attrname,attrvalue)
  nodeAttr(prefix:name,namespace,expr,...)
  struct(prefix,namespace)

Both of these ideas were abandoned because it was too complicated to
implement (requiring changes to the handling of perl attributes).

I went ahead with the "shorthand" namespace declaration idea because
it extends the node name parameter to include both the prefix and the
namespace:

  node(prefix:name:namespace)
  nodelist(prefix:name:namespace)
  exprOrNode(prefix:name:namespace,attrname,attrvalue)
  exprOrNodelist(prefix:name:namespace,attrname,attrvalue)
  nodeAttr(prefix:name:namespace,expr,...)
  struct(prefix,namespace)

which means I did not have to modify how the perl attributes were
processed--I just had to modify how the node name was processed.

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