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      <h1>Extensibility</h1>
      <p>The Saxon XQuery implementation allows you to call Java methods as external functions.
The function does not need to be declared. Use a namespace declaration such as 
<code>declare namespace math="java:java.lang.Math"</code>,
and invoke the method as <code>math:sqrt(2)</code>.</p>
      <p>More details of this mechanism are found in 
<a class="bodylink" href="../extensibility/functions.xml">Writing Extension Functions</a>; note however
that for XQuery the only form of namespace URI accepted is <code>java:<i>full.class.Name</i></code>.</p>
      <p>Saxon recognizes the XQuery pragma syntax, but it currently defines only one pragma of its own,
the <code>saxon:validate-type</code> pragma (see <a class="bodylink" href="../using-xquery/extensions.xml">Extensions</a>).
Saxon will adopt the correct fallback behavior if presented with a query that uses another
vendor's extensions, provided these are designed in conformance with the W3C pragma specification.</p>
      <p>Saxon also recognizes the XQuery option declaration syntax. Several specific option declarations are
provided: <code>declare option saxon:default</code> declares a default value for external variables
(query parameters); <code>declare option saxon:output</code> declares a serialization parameter;
and <code>declare option saxon:memo-function</code> defines whether the following function declaration is
to be implemented as a memo function.
These are described under <a class="bodylink" href="../using-xquery/extensions.xml">Extensions</a>. Any other option declaration in the
Saxon namespace is ignored with a warning; an option declaration in any other namespace is ignored silently.</p>
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