<term><structfield>type</structfield></term>
      <listitem>
       <para>
        Always <literal>T_TriggerData</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_event</structfield></term>
      <listitem>
       <para>
        Describes the event for which the function is called. You can use the
        following macros to examine <literal>tg_event</literal>:

        <variablelist>
         <varlistentry>
          <term><literal>TRIGGER_FIRED_BEFORE(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger fired before the operation.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>TRIGGER_FIRED_AFTER(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger fired after the operation.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>TRIGGER_FIRED_INSTEAD(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger fired instead of the operation.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>TRIGGER_FIRED_FOR_ROW(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger fired for a row-level event.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>TRIGGER_FIRED_FOR_STATEMENT(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger fired for a statement-level event.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>TRIGGER_FIRED_BY_INSERT(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger was fired by an <command>INSERT</command> command.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>TRIGGER_FIRED_BY_UPDATE(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger was fired by an <command>UPDATE</command> command.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>TRIGGER_FIRED_BY_DELETE(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger was fired by a <command>DELETE</command> command.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>TRIGGER_FIRED_BY_TRUNCATE(tg_event)</literal></term>
          <listitem>
           <para>
            Returns true if the trigger was fired by a <command>TRUNCATE</command> command.
           </para>
          </listitem>
         </varlistentry>
        </variablelist>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_relation</structfield></term>
      <listitem>
       <para>
        A pointer to a structure describing the relation that the trigger fired for.
        Look at <filename>utils/rel.h</filename> for details about
        this structure.  The most interesting things are
        <literal>tg_relation-&gt;rd_att</literal> (descriptor of the relation
        tuples) and <literal>tg_relation-&gt;rd_rel-&gt;relname</literal>
        (relation name; the type is not <type>char*</type> but
        <type>NameData</type>; use
        <literal>SPI_getrelname(tg_relation)</literal> to get a <type>char*</type> if you
        need a copy of the name).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><structfield>tg_trigtuple</structfield></term>
      <listitem>
       <para>
        A pointer to the row for which the trigger