Parser compliance

David Megginson david at
Wed Nov 17 22:39:20 GMT 1999

Richard Lanyon <rgl at> writes:

> Anyway, the point is that the issue of different XML document
> layouts for different parsers is not merely one of conformance, but
> of the number of optional features as well (something particularly
> telling in the light of the cut-down XML debate currently continuing
> on this list).

Yes, I agree -- in retrospect, it was a technical mistake to allow so
many optional features in XML, though that mistake is really just an
annoyance to us techies and hasn't inhibited the spread of XML in the
wider world, at least not yet.

Off the cuff, I can think of the following major optional features in
the XML 1.0 REC:

1. Validation
2. Inclusion of external general entities (if non-validating)
3. Inclusion of external parameter entities (if non-validating)

Since many major specs now rely on Namespaces, you can add

4. Namespace processing

(even though that's not part of XML 1.0).  Furthermore, validation
needs to be broken down quite a bit: for example, a non-validating
processor may still read element type declarations and distinguish
whitespace in element content (as AElfred does) and may still perform
ID/IDREF verification.

All the best,


David Megginson                 david at

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