Sometimes documents need to include specific values for particular
content. The value
pattern can check fixed values, such as version identifiers of XML
vocabularies. The syntax and semantics of the
value
pattern are straightforward: the pattern is
matched only if the value found in the instance document matches the
value specified in the value
pattern. For example,
if you want a highly specialized vocabulary to describe the book with
the ISBN number 0836217462 and only this specific book, you can
replace the text
pattern with a
value
pattern and write:
<element name="isbn"> <value>0836217462</value> </element>
or, using the compact syntax:
element isbn {"0836217462"}
and the schema will validate a book with a ISBN number equal to 0836217462 and refuse any other ISBN number.
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