be zero.
         As a special case, -1 indicates a NULL column value.
         No value bytes follow in the NULL case.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Byte<replaceable>n</replaceable></term>
       <listitem>
        <para>
         The value of the column, in the format indicated by the
         associated format code.
         <replaceable>n</replaceable> is the above length.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </listitem>
   </varlistentry>

   <varlistentry id="protocol-message-formats-Describe">
    <term>Describe (F)</term>
    <listitem>
     <variablelist>
      <varlistentry>
       <term>Byte1('D')</term>
       <listitem>
        <para>
         Identifies the message as a Describe command.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Int32</term>
       <listitem>
        <para>
         Length of message contents in bytes, including self.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Byte1</term>
       <listitem>
        <para>
         '<literal>S</literal>' to describe a prepared statement; or
         '<literal>P</literal>' to describe a portal.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>String</term>
       <listitem>
        <para>
         The name of the prepared statement or portal to describe
         (an empty string selects the unnamed prepared statement
         or portal).
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </listitem>
   </varlistentry>

   <varlistentry id="protocol-message-formats-EmptyQueryResponse">
    <term>EmptyQueryResponse (B)</term>
    <listitem>
     <variablelist>
      <varlistentry>
       <term>Byte1('I')</term>
       <listitem>
        <para>
         Identifies the message as a response to an empty query string.
         (This substitutes for CommandComplete.)
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Int32(4)</term>
       <listitem>
        <para>
         Length of message contents in bytes, including self.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </listitem>
   </varlistentry>

   <varlistentry id="protocol-message-formats-ErrorResponse">
    <term>ErrorResponse (B)</term>
    <listitem>
     <variablelist>
      <varlistentry>
       <term>Byte1('E')</term>
       <listitem>
        <para>
         Identifies the message as an error.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>Int32</term>
       <listitem>
        <para>
         Length of message contents in bytes, including self.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>

     <para>
      The message body consists of one or more identified fields,
      followed by a zero byte as a terminator.  Fields can appear in
      any order.  For each field there is the following:
     </para>

     <variablelist>
      <varlistentry>
       <term>Byte1</term>
       <listitem>
        <para>
         A code identifying the field type; if zero, this is
         the message terminator and no string follows.
         The presently defined field types are listed in
         <xref linkend="protocol-error-fields"/>.
         Since more field types might be added in future,
         frontends should silently ignore fields of unrecognized
         type.
        </para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>String</term>
       <listitem>
        <para>
         The field value.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </listitem>
   </varlistentry>

   <varlistentry id="protocol-message-formats-Execute">
    <term>Execute (F)</term>
    <listitem>
     <variablelist>
      <varlistentry>
       <term>Byte1('E')</term>