[xml-dev] Compatibility for XML attribute types with schemas

[Elliotte Rusty Harold <elharo@metalab.unc.edu>]

Most of the XML simple types in the W3C XML Schema Language -- e.g. 
NOTATION, NMTOKEN, iD, IDREF, etc. -- carry a compatibility rule; for 
example:

For compatibility (see Terminology (§1.4) 
<http://www.w3.org/TR/xmlschema-2/#terminology> ) *NMTOKEN* should be 
used only on attributes.

How important is this? Would it really be a compatibility problem to say 
that an element must have type NMTOKEN? or be an ID? How would this be 
incomaptible with standard XML? The resulting document would still be 
well-formed and perhaps DTD valid. Nothing in the schema would change 
this. Of course, these constraints could not be used on elements in a 
DTD. However, netiher could a constraint that an element be required to 
contain an integer, whihc is acceptable in schemas.

What's the reasoning  here? Why shouldn't we use NMTOKEN and the like 
for element types?

-- 
+-----------------------+------------------------+-------------------+
| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
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|               Java I/O (O'Reilly & Associates, 1999)               |
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