Undeclared elements error

[Richard L. Goerwitz III]

> Liam R. E. Quin wrote:
> 
> > Should the following produce a warning?
> > 
> >     <!ELEMENT CHAPTER (LOCATION,DESCRIPTION)>
> >     <!--* error: LOCATION has not been declared *-->
> >     <!--* error: DESCRIPTION has not been declared *-->
> > 
> >     <!ELEMENT LOCATION (#PCDATA)>
> >     <!ELEMENT DESCRIPTION (#PCDATA)>
> 
> Absolutely not.

In an attempt to flesh out James Clark's somewhat abrupt note, let
me just give you a quick example illustrating why your intuitions
were right about it being okay to use element names in content models
before they are declared:

  <!ELEMENT text (#PCDATA | italic | bold)*>
  <!ELEMENT italic (#PCDATA | bold)*>
  <!ELEMENT bold (#PCDATA | italic)*>

Other questions you might wonder about include:

  1) What if I use an element in a content model and I don't
     declare it?
  2) What if I declare an element in a content model that I
     don't use in any content model (and the element isn't the
     root element)?

By my reading of the XML spec, these are not clearly stated to be
errors.  So they aren't errors (unless you try to use the elements
in a document - in which case, other constraints exclude them).

I may have missed something, of course.

In such situations, it's tempting to cheat and just use your know-
ledge of SGML.  One would hope that future standards will answer
such questions definitively, removing this temptation (confusion).

Richard Goerwitz
STG


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