xml-dev - Empty AttlistDecl

[David Megginson <ak117@freenet.carleton.ca>]

Stefan Mintert writes:

 > What's the purpose of an empty AttlistDecl?
 > Shouldn't production [52] read instead as follows?
 > 
 >        AttlistDecl ::= '<!ATTLIST' S Name AttDef+ S? '>'
 > 
 > (+ instead of *)

Actually, it turns out to be remarkably useful for external DTD
subsets.  Consider this:

  <![%security;[
    <!ENTITY % security-atts "
      level CDATA #REQUIRED
      auth CDATA #REQUIRED">
  ]]>
  <!ENTITY % security-atts "">

  <!ATTLIST section %security-atts;>

Now, if the %security; parameter entity is set to "INCLUDE" (to enable
security features), you will get

  <!ATTLIST section
    level CDATA #REQUIRED
    auth CDATA #REQUIRED>

If the %security; parameter entity is set to "IGNORE" (to disable
security features), you will get

  <!ATTLIST section>

Fortunately, this is still legal in XML.


All the best,


David

-- 
David Megginson                 ak117@freenet.carleton.ca
Microstar Software Ltd.         dmeggins@microstar.com
      http://home.sprynet.com/sprynet/dmeggins/

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