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<td valign="top" class="NAME">Parameter Entities</td>
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<p>The 
parameter entity mechanism is a
simple macro replacement facility that is only valid within the
context of the DTD. Parameter entities are declared and then
referenced from within the DTD or possibly from within other entity
declarations. The source of the entity replacement text can be either
a literal string or the contents of an external file. Parameter
entities simplify maintenance of large, complex documents by allowing
authors to build libraries of commonly used entity declarations.</p>
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