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

David Megginson dmeggins at uottawa.ca
Mon Apr 21 12:58:36 BST 1997

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)*

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

All the best,


David Megginson                 ak117 at freenet.carleton.ca
Microstar Software Ltd.         dmeggins at microstar.com
University of Ottawa            dmeggins at uottawa.ca

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