DOM design

David Megginson ak117 at
Wed Dec 31 12:29:58 GMT 1997

Gavin Nicol writes:

 > >Perhaps both comments and general entity references belong more
 > >properly in a level-two DOM rather than in level one, since they deal
 > >with lexical issues rather than logical structure.
 > I, for one, believe comments to be part of the *structure* of a document.

Technically, this is not the case.  An SGML or XML document has only
two well-defined structures:

1) the logical (element/attribute/data) structure; and

2) the physical (entity) structure.

The presence or absence of a comment has no effect on either of these,
so like CDATA sections and PIs, comments are not structural.

However, as has become clear in this discussion, many people do
believe that comments are a significant part of an XML document's
information set.  That is certainly a legitimate view, but since
comments are non-structural, they should not _automatically_ qualify
for inclusion; instead, someone needs to make a strong case for them,
as I have tried to do for PIs (also non-structural) in SAX-J.

It still seems to me that it would make much more sense for the
level-one DOM to cover only logical structure + PIs (the minimum
needed to process XML documents for formatting, online transactions,
etc.), while a level-two DOM could cover the physical structure and
lexical items needed for editors and repositories (comments, entity
references, ignored whitespace, etc.).  Sticking everything into the
level-one DOM muddies the whole thing unnecessarily.

All the best,


David Megginson                 ak117 at
Microstar Software Ltd.         dmeggins at

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