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Can I use an attribute default in a DTD to declare an XML namespace?
XML Interview Questions and Answers
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67. Can I use an attribute default in a DTD to declare an XML namespace?
Yes.
For example, the following uses the FIXED attribute xmlns:google on the A element type to associate the google prefix with the http://www.google.org/ namespace. The effect of this is that both A and B are in the http://www.google.org/ namespace.
<?xml version="1.0" ?>
<!DOCTYPE google:A [
<!ELEMENT google:A (google:B)>
<!ATTLIST google:A
xmlns:google CDATA #FIXED "http://www.google.org/">
<!ELEMENT google:B (#PCDATA)>
]>
<!-- google prefix declared through default attribute. -->
<google:A>
<google:B>abc</google:B>
</google:A>
IMPORTANT: You should be very careful about placing XML namespace declarations in external entities (external DTDs), as non-validating parsers are not required to read these. For example, suppose the preceding DTD was placed in an external entity (google.dtd) and that the document was processed by a non-validating parser that did not read google.dtd. This would result in a namespace error because the google prefix was never declared:
<?xml version="1.0" ?>
<!-- google.dtd might not be read by non-validating parsers. -->
<!DOCTYPE google:A SYSTEM "google.dtd">
<!-- google prefix not declared unless google.dtd is read. -->
<google:A>
<google:B>abc</google:B>
</google:A>
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