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Logic for extending text XML elements

From: Lisa Dusseault <lisa@xythos.com>
Date: Tue, 5 Jun 2001 09:28:38 -0700
To: <w3c-dist-auth@w3.org>
Message-ID: <HPELJFCBPHIPBEJDHKGKGECFCGAA.lisa@xythos.com>
I've run into a minor issue relating to XML syntax and WebDAV extensibility.

I'm parsing:
<D:href>http://myserver.com/</D:href>

Since an XML element can legally contain both text and elements (e.g.
<P>Hello <em>sailor!</em></P>), it's conceivable that in the future the
<href> element could be extended to have:

<D:href>http://myserver.com/
  <expires>123486</expires>
  more-stuff
</D:href>

RFC 2518 says:
   "All DAV compliant resources MUST ignore any unknown XML element and
   all its children encountered while processing a DAV method that uses
   XML as its command language."

That would indicate that I should ignore the <expires> element.  I can do
that.  But what does "ignore" mean?
 - Do I treat it as a separator so that "http://myserver.com/" is one text
child of DAV:href and "more-stuff" is another text child?  How do I know
which one to treat as the URL, particularly if they both look like urls?
 - Do I conceptually remove the ignored element?  That would leave
<DAV:href> with a single text child containing white space, approximately:
"http://myserver.com/  more-stuff".

Since all this is rather ugly, I'd most like to have a sentence added to RFC
2518 (section 14?) that states at a minimum that "text elements should NOT
have their syntax extended by adding XML elements because this is unlikely
to be backward-compatible."  I think we already instinctively follow this
guideline, but it's hard to write solid code based on guesses and
predictions that aren't written down.

Any other proposals or insights?

lisa
Received on Tuesday, 5 June 2001 12:30:06 GMT

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