built-in shelf
#xmlns-names is a built in read-only stream shelf displaying the currently active set
of XML namespace/prefix mappings. The keys on the shelf are the element prefixes, and the values are the
corresponding namespace names (URIs).
While parsing the content of the following element
<a xmlns:omdoc="http://www.omnimark.com/docs/"
xmlns:omtbl="http://www.omnimark.com/table.dtd">
the shelf will contain
omdoc and value http://www.omnimark.com/docs/, and
omtbl and value http://www.omnimark.com/table.dtd/.
A namespace name consisting of a zero length string indicates the absence of a namespace. Encountering this explicitly causes the prefix to be removed from the shelf if it already exists, or otherwise simply not added.
When parsing the instance
<a xmlns:foo="bar">
<b xmlns:foo="">
Immediately following the start tag for a, the #xmlns-names shelf has an
entry with key foo and value bar. Inside element b, this shelf item is
removed. After the end of element b (but still within element a) the shelf item will
be restored.
The default namespace is represented by a shelf item with the empty string as the key.
<a xmlns="foo">
The #xmlns-names shelf is saved before each start tag, and restored after each end tag. The shelf is
saved and cleared at the start of each markup-parse.