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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>bool</type><methodname>xml_set_processing_instruction_handler</methodname>
     <methodparam><type>resource</type><parameter>parser</parameter></methodparam>
     <methodparam><type>callback</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>resource</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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