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- From: Lars Marius Garshol <email@example.com>
- To: "'XML Dev'" <firstname.lastname@example.org>
- Date: 11 Nov 1998 23:52:02 +0100
* Don Kackman
| I've got two document types with associated DTDs. The first is a subset
| of the second. I don't want to merge these two DTDs into one file but
| also don't want to maintain both files seperately.
| Is it possible to include one DTD in another through an external entity
| reference? If so how?
In file sub-dtd.dtd:
[...lots of declarations...]
<!ENTITY % base-dtd SYSTEM "base-dtd.dtd">
where the file base-dtd.dtd contains the declarations common to both
You will probably have some problems with content models when you try
this if sub-dtd.dtd contains element declarations. If so, it may be
helpful for you to know that section 4.2 of the spec says: "If the
same entity is declared more than once, the first declaration
encountered is binding; at user option, an XML processor may issue a
warning if entities are declared multiple times."
This can be used to make 'hooks' in content models where sub-DTDs can
insert the new elements they introduce.
| Also if so, can I declare additional attributes in the second DTD
| for elements originally declared in the first?
Yes, the XML spec explicitly provides for this. In section 3.3 it
says: "When more than one AttlistDecl is provided for a given element
type, the contents of all those provided are merged."
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