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Denoting an XML document that obeys the syntax rules for markup laid down by the XML standard. For example, every non-empty opening tag must be balanced by an equivalent closing tag; there must be a single root element; and elements must be properly nested and not overlap. To be well-formed is the basic requirement for any XML document; XML software expects this and will usually reject any document that is not. Associating a DTD or XML schema with a document adds a second requirement, that in addition to being well-formed the document's usage of XML markup should be limited to the structure specified in the DTD or schema. It is thus possible for a document to be well-formed but not conform to its DTD; the reverse, however, is not possible. (For this reason “well-formedness” is not a useful concept in SGML, where all documents must have a DTD.)

Subjects: Computing.

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