#PCDATA in model group that is not optional and repeatable (was: XML and repeatable model groups)

[David Megginson]

geirog at falch.no writes:

 > >By the way, you gain nothing by using "+" instead of "*", since
 > >#PCDATA can be an empty string.  
 > 
 > I know, but why isn't it allowed at all? (or why was it allowed in SGML in
 > the first place?)

Because full SGML treats all content models equally, while XML
attaches special restrictions to those with mixed content.  Full SGML
also allows relatively useless expressions like

  (#PCDATA & foo)*
  (#PCDATA)+

and it will let you do many other strange things, as long as your
content model does not become ambiguous.


All the best,


David

-- 
David Megginson                 ak117 at freenet.carleton.ca
Microstar Software Ltd.         dmeggins at microstar.com
University of Ottawa            dmeggins at uottawa.ca
        http://www.uottawa.ca/~dmeggins

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