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Al B. Snell wrote: > Quite a few schemas now have provision for comments, which can do stuff > like import from XHTML or DocBook namespaces. This clearly allows for rich > comments, unlike <!-- --> comments. Does this mean that <!-- --> comments > should be discouraged Features like the W3C schema's annotation element are clearly a step up from using XML 1.0 (<!-- -->) comments in DTDs, because they'll make it possible to throw together automated processes to create more useful documentation of schemas, as with Java's javadoc. > <!-- --> comments, like <?foo ?> PIs, seem to be one of those bits of XML > that nobody ever uses. At least, I never see them in the coding examples > around here. Oh yeah, and that <!NOTATION > thing is a bit of a pariah, > too... XML 1.0 comments work in both DTDs and documents, and commenting any kind of code is always a Good Thing, and people rarely use it as much as they should. I've seen programming books that encourage you to comment your code and then don't comment their own code samples. XML 1.0 comments are for whatever you want them to be for; for example, if I write something that generates XML output, I usually start that output with an XML comment that has a time stamp, the name of the generating program, etc. In an XML document that I'm hand-editing, I'll have a comment that shows the last date edited andmaybe a to-do list concerning the work I'm doing on it. It's also a place to store version control information for use by a package like rcs. Processing instructions and NOTATION declarations are a different story. XML inherited both from SGML, where PIs were usually used as a way to store information for some non-SGML application that was going to process the document. Now that XML support is so ubiquitous and so easy to add to applications that need it, this becomes less and less relevant. NOTATION declarations were one of the steps that were necessary to refer to non-SGML/XML data (e.g. binary files), and while more and alternatives are showing up now (e.g. the W3C schemas' hexBinary and base64Binary data types), when the XML spec was being in 1997, unparsed entities were the only way to do this. >does anybody use entities to refer to stuff in favour of <foo > href="..." />, anyway? The latter seems much more convenient, since it > doesn't require all definitions to be gathered inside the <!DOCTYPE >... Yes, more convenient. The entities way is more work, but theoretically that work buys you more data integrity, because the XML parser is required to resolve the entity reference and make sure that the referenced file is really there. Bob DuCharme www.snee.com/bob <bob@ snee.com> see http://www.snee.com/bob/xsltquickly for info on upcoming "XSLT Quickly" from Manning Publications.
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