There seem to be two camps of user of the ExtensibleMarkupLanguage:

	1. XMLers who want to use XmlSchema''''''s and DocumentTypeDefinition''''''s

	2. XMLers who want to use XML to record self schematizing data, where every data item collected may have ad-hoc fields and notes, and where updating a central schema would be wasted time.

XML is a self schematizing data format, that allows such ad-hoc
structure to be recorded in a slightly better way than simply 
recording everything as raw text.  
Generic non-DTD based XML tools can perform many useful queries
on such data.
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CategoryXml