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   Re: <!ELEMENT C (A,A)> allowed?

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  • From: Eric Bohlman <ebohlman@netcom.com>
  • To: "Schoedl, Andreas" <Andreas.Schoedl@softwareag.com>
  • Date: Wed, 31 May 2000 08:40:31 -0700 (PDT)

On Wed, 31 May 2000, Schoedl, Andreas wrote:

> <!ELEMENT C (A,A)>, is such content model allowed? I ask, because I can
> nowhere find the statement that it is forbidden. But I strongly feel that it
> should be! 


> Whereas <!ELEMENT C (A?,A)> seems to be excluded (XML REC 3.2.1), alas not
> _very_ explicitly.

Because the content model is ambiguous.  When the processor sees the first
<A> after a <C>, it can't tell whether it's the first or second item in
the sequence without looking ahead.  Note that (A,A?) describes the same
language but is not ambiguous.

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