an xslt question re modeling namespaces

[james anderson <james.anderson@mecomnet.de>]

The "XSL Transformations" working draft (WD-xslt11-20001212) contains
the following passage under the heading "Namespace Fixup". I am curious.
Are these xslt-specific constraints? Do they derive from one of the data
models? 



"In a tree constructed by parsing an XML document, the following
constraints relating to namespace nodes will be satisfied:

  If an element node has an expanded-name with a non-null namespace URI,
then that element node will have at least one namespace node whose
string-value is the same as that namespace URI.

  If an attribute node has an expanded-name with a non-null namespace
URI, then the parent element of that attribute will have at least one
namespace node whose string-value is the same as that namespace URI and
whose expanded-name has a non-empty local part.

  If an element node has a namespace node with an expanded-name with a
non-empty local part, then every child element of that element will also
have a namespace node with that expanded-name (possibly with a different string-value).

   Every element has a namespace node whose expanded-name has local-part
xml and whose string-value is http://www.w3.org/XML/1998/namespace."