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  <refentry id="function.xml-set-processing-instruction-handler">
   <refnamediv>
    <refname>xml_set_processing_instruction_handler</refname>
    <refpurpose>
     Set up processing instruction (PI) handler
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>int</type><methodname>xml_set_processing_instruction_handler</methodname>
      <methodparam><type>int</type><parameter>parser</parameter></methodparam>
      <methodparam><type>string</type><parameter>handler</parameter></methodparam>
     </methodsynopsis>
    <para>
     Sets the processing instruction (PI) handler function for the XML
     parser <parameter>parser</parameter>.
     <parameter>handler</parameter> is a string containing the name of
     a function that must exist when <function>xml_parse</function> is
     called for <parameter>parser</parameter>.
    </para>
    <para>
     A processing instruction has the following format:
     <informalexample>
      <programlisting>&lt;?
       <replaceable>target</replaceable> 
       <replaceable>data</replaceable>?>
      </programlisting>
     </informalexample>
     You can put PHP code into such a tag, but be aware of one
     limitation: in an XML PI, the PI end tag
     (<literal>?&gt;</literal>) can not be quoted, so this character
     sequence should not appear in the PHP code you embed with PIs in
     XML documents.  If it does, the rest of the PHP code, as well as
     the "real" PI end tag, will be treated as character data.
    </para>
    <para>
     The function named by <parameter>handler</parameter> must accept
     three parameters:
     <methodsynopsis>
       <methodname><replaceable>handler</replaceable></methodname>
       <methodparam><type>int</type><parameter>parser</parameter></methodparam>
       <methodparam><type>string</type><parameter>target</parameter></methodparam>
       <methodparam><type>string</type><parameter>data</parameter></methodparam>
     </methodsynopsis>
     <variablelist>
      <varlistentry>
       <term><parameter>parser</parameter></term> <listitem><simpara>
       The first parameter, <replaceable>parser</replaceable>, is a
       reference to the XML parser calling the
       handler.</simpara></listitem>
      </varlistentry>
      <varlistentry>
       <term><parameter>target</parameter></term>
       <listitem><simpara>
     The second parameter, <parameter>target</parameter>, contains
     the PI target.</simpara></listitem>
      </varlistentry>
      <varlistentry>
       <term><parameter>data</parameter></term>
       <listitem><simpara>
     The third parameter, <parameter>data</parameter>, contains
     the PI data.</simpara></listitem>
      </varlistentry>
     </variablelist></para>
    <para>
     If a handler function is set to an empty string, or
     &false;, the handler in question is disabled.
    </para>
    <para>
     &true; is returned if the handler is set up, &false; if
     <parameter>parser</parameter> is not a parser.
    </para>
    &note.func-callback;
   </refsect1>
  </refentry>

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