🚀 go-pugleaf

Hey folks,

I've I problem with the operator precedence in SGML.

I parsed an incorrect (?) SGML file with the markit 2.0 parser, but no
error message or warning occurs.

The problem in detail:

When the DTD has following element definition

<!ELEMENT x - - (z, (a* | b*)) >

(with the intention to allow a z followed by repeatative a's OR repeatative b's)

and the sgml instance looks like this

	<x>
	<z>...</z>
	<a>...</a>
	<b>...</b>        <------- !!! Error !!! ------->
	<a>...</a>
	</x>

the markit says, that it is okay.

When I change the element definition to

	<!ELEMENT x - - (z, ((a*) | (b*))) >
	                     -  -   -  -

the markit prints an error message for the "b" tag, what I expected already with
the first definition.

Is this a bug of the markit or is my interpretation of the operator precedence
in SGML wrong?

Is the first element definition equivalent to

	<!ELEMENT x - - (z, ((a* | b)*)) > ???
	                     _      _

I don't think so and Mr. Martin Bryan in "SGML an Author's Guide", page 111 don't
think so, too.

I always thought, that the occurence indicators ("?", "+", "*") have a higher
precedence than the group connectors ("|", ",", "&").

What do the experts think about these problems?


Thanks in advance,

--Holger


P.S.: I wish everybody an HAPPY NEW YEAR.

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| Hans Holger Rath - Computer Graphics Center - Darmstadt - Germany |
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