SUMMARY: XML Validation Issues (was: several threads)

Jelks Cabaniss jelks at
Mon Apr 12 20:01:58 BST 1999

Chris Lilley wrote:

> > > My feeling is that there are three classes of implementation, that
> > > should all have names:
> > >
> > > minimal well-formed - never tries to follow external entities
> > > full well-formed - always tries to follow external entities
> > > full validating - always tries to follow external entities and validates

> > Agreed. ...

> > > and it should be possible to always derive what class of implementation
> > > a particular instance requires.

> You don't comment on that sentence, so does it mean you agree?

Yes.  But see below.

> > If there is to be a way to *force* validity by specifying it in the document
> > instance, the only way I can see is by amending the spec with
> > something like (as I believe you yourself suggested in passing)
> > valid="yes" in the declaration.
> Right. With a default of "no", of course. So, this would make the
> assertion that the document was valid and that assertions could be
> tested and perhaps refuted, by a validating parser. In the case of
> "valid="no" or perhaps, valid="wf", a validating parser would do what -
> declare the document invalid? Agree, yes, its invalid (so why check it)?
> Automatically use a non-validating mode, even if it was normally
> validating?

> Next question, should there be (in other words, is this something that
> should be in the document instance).


But how to do it?  If XML 1.1 has a "valid='yes'|'no'" in the declaration, XML
1.1 documents may break when running under an XML 1.0 parser, since the XML 1.0
BNF clearly states what can and can't be in the declaration.

Maybe a PI could be formalized similar to the way the stylesheet linking is
being done:

	<?xml-assert implementation="valid"?>

(could also be "minimal" or "full" for the well-formed only options you


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