3 XML Base questions

["Roger L. Costello" <costello@mitre.org>]

I have 3 questions on XML Base:

1. My first question is to make sure that I understand the big picture: 
It is my understanding that a specification will define whether or not
it supports XML Base, and if it does, it will define where (on what
elements) the xml:base URL can be applied.  For example, the XLink
specification says (my own words) "yes, we support XML Base; any href in
an XLink that has a relative URL will have the xml:base URL prepended". 
That is, a specification identifies where an xml:base URL may be
applied.  Contrast with a specification (A) that does not support XML
Base, then any A-aware tool is not expected to understand xml:base, and
will not do any URL-prepending.  Is this the way it works?

2. Assuming my statements in (1) are correct, then I would like to know
what specifications currently support XML Base, and what elements have
they identified as being XML Base-able.  Here's my initial stab at a
list:

Specification         XML Base-able elements
-----------------------------------------------------
HTML/XHTML            the href in an anchor element
                      the src in an image element

XInclude              the href in an include element

XLink                 the href in an XLink element

XML Schemas           the schemaLocation attribute
                      the noNamespaceSchemaLocation attribute
                      the targetNamespace attribute
                      (I am currently getting clarification on whether
                       these schema attributes are XML Base-able, so 
                       don't take this as gospel.  If anyone knows
                       with certainty please let me know.)


Are there other specifications which support XML Base?  What about RDDL?
RDF?

3. With namespaces you can declare a namespace and use it, all in one
fell swoop.  For example:

   <c:Camera xmlns:c="http://www.camera.org";>

Notice how I declared the namespace (and the prefix, c) on the Camera
element, and simultaneously qualified Camera.

Can we similarly declare an xml:base URL and use the xml:base URL?  For
example:

   <BookCatalogue xml:base="http://www.example.org/";
                  xsi:schemaLocation="http:books.org
                                      BookCatalogue.xsd"
                  ...>

Note how I declared the xml:base URL (http://www.example.org/) and
simultaneously used the xml:base URL in schemaLocation.  Thus, the
complete schemaLocation is: http://www.example.org/BookCatalogue.xsd. 
Is this legal - declare the xml:base URL and use it simultaneously?

Thanks!  /Roger