On Thu, Aug 6, 2009 at 11:11 AM, Liam Quin <liam@w...> wrote:
> You only need to list those elements that can occur embedded in another
> vocabulary, plus the top-level element.  For example, a list item might
> not make sense without a containing list.  So, a docbook list would
> automatically introduce the docbook namespace for all the elements it
> contained (until you got down to ones that implied some other
> namespace, such as "svg" perhaps).

I think it would be useful, in other contexts as well, to have a list
of elements from a particular vocabulary that the vocabulary's
designer baptizes as making sense to embed within another vocabulary.
(Specifically, such an element E in vocabulary N could be called a
boundary element, and a document D would be boundary-valid iff for
every element E', if the parent of E' is in a different vocabulary,
then E' is a boundary element.)  This provides a sort of light weight
validation for compound documents.  It also might be semantically
interesting to see how elements fall into the two different coarse
categories.

Of course, this assumes that elements have consistent local semantics
wherever they're found in a vocabulary, but this is not necessarily
the case.  For example, you could have a 'warning' element that has
different weight in different contexts.  Perhaps such
context-sensitive elements are always non-boundary elements, though.

Take care,

    John L. Clark

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