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Subject:Re: XML ELEMENT value required? From:"Mark Baker" <listsub -at- analecta -dot- com> To:"TECHWR-L" <techwr-l -at- lists -dot- raycomm -dot- com> Date:Fri, 2 Apr 2004 16:12:58 -0500
David Spreadbury wrote:
> Ned's question was:
>
> "... can I force an XML element's value to be required ?"
>
> Not if the value was valid.
>
> The way I understand XML, is if the DTD "requires" an attribute, whether
it is a valid
> attribute or not, there better be an attribute there.
True, but there is a difference between an element and an attribute. Ned did
not ask about attributes, he asked about elements. The term "value of an
element" which is not strict XML terminology, is generally understood to
mean its data content. (If Ned means something else, then he needs to
clarify.) There is no way to require that an element have data content, or
rather to be precise, if an element is declared with a content model of
#PCDATA, that content model can be satisfied by an empty string, and there
is no way to require that it be anything more than an empty string.
Note also that there is a difference between requiring an attribute to exist
and requiring it to have a value. A DTD can do both of these things, but
what #REQUIRED does is require that an attribute exist, not that it have a
value. If you specify an attribute as CDATA #REQUIRED, the CDATA requirement
can be met by an empty string. So, you can specify:
<!element actor #PCDATA>
<!attlist actor name CDATA #REQUIRED>
But you cannot (with a CDATA attribute) make the parser object if it sees:
<actor name=""></actor>
Which is what I believe Ned is asking for.
---
Mark Baker
Analecta Communications
www.analecta.com
+1 613 614 5881
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