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   Re: Parser Question.

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  • From: Eric Bohlman <ebohlman@netcom.com>
  • To: "Brown, Bryan" <bryanb@upshot.com>
  • Date: Wed, 31 May 2000 19:34:52 -0700 (PDT)

On Wed, 31 May 2000, Brown, Bryan wrote:
> In the external subset PEs can occur anywhere, this seems to me to make the
> process of parsing an external production very complicated because I need to
> check at each step of the way if the next token is a PE reference, does
> anyone have a better way ? Why is this allowed in the spec is there really
> that much value in being able to specify
> <!ENTITY % e2 "(e3|e4)">
> <!ELEMENT e2 %e2;>
> instead of
> <!ENTITY % e2 "<!ELEMENT e2 (e3|e4)>">
> %e2;
> Seems to me that is the same effect without having to make a parser
> implementors life a hell of alot more difficult.

Take a look at any of the HTML DTDs in either SGML or XML to see a good
example of how useful this ability is.  IIRC, the only reason that
parameter entities in the internal subset have to expand to full markup
declarations is that otherwise a non-validating parser that was processing
an internal declaration that incorporated an external parameter entity
(that the parser did not expand) might be confronted with a syntactically
illegal declaration.

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