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case-sensitive
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well-formedness
constraints (partial list)
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every
element must have start tag and end tag
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elements
must be correctly nested
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attribute
values must be quoted (matching single or
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double)
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XML
parser checks XML document to make sure
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that
[1] it is well-formed (complies with all w.f.
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constraints
in specification), and [2] it is valid,
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meaning
the tag names and order conform to the
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XML
application’s Document Type Definition
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(DTD)—the
definition of what tags it may have and
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in
what order
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