<parameter>count</parameter> <type>integer</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Replaces the substring of <parameter>string</parameter> that starts at
        the <parameter>start</parameter>'th character and extends
        for <parameter>count</parameter> characters
        with <parameter>newsubstring</parameter>.
        If <parameter>count</parameter> is omitted, it defaults to the length
        of <parameter>newsubstring</parameter>.
       </para>
       <para>
        <literal>overlay('Txxxxas' placing 'hom' from 2 for 4)</literal>
        <returnvalue>Thomas</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>position</primary>
        </indexterm>
        <function>position</function> ( <parameter>substring</parameter> <type>text</type> <literal>IN</literal> <parameter>string</parameter> <type>text</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns first starting index of the specified
        <parameter>substring</parameter> within
        <parameter>string</parameter>, or zero if it's not present.
       </para>
       <para>
        <literal>position('om' in 'Thomas')</literal>
        <returnvalue>3</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>rpad</primary>
        </indexterm>
        <function>rpad</function> ( <parameter>string</parameter> <type>text</type>,
        <parameter>length</parameter> <type>integer</type>
        <optional>, <parameter>fill</parameter> <type>text</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Extends the <parameter>string</parameter> to length
        <parameter>length</parameter> by appending the characters
        <parameter>fill</parameter> (a space by default).  If the
        <parameter>string</parameter> is already longer than
        <parameter>length</parameter> then it is truncated.
       </para>
       <para>
        <literal>rpad('hi', 5, 'xy')</literal>
        <returnvalue>hixyx</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>rtrim</primary>
        </indexterm>
        <function>rtrim</function> ( <parameter>string</parameter> <type>text</type>
         <optional>, <parameter>characters</parameter> <type>text</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Removes the longest string containing only characters in
        <parameter>characters</parameter> (a space by default) from the end of
        <parameter>string</parameter>.
       </para>
       <para>
        <literal>rtrim('testxxzx', 'xyz')</literal>
        <returnvalue>test</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>substring</primary>
        </indexterm>
        <function>substring</function> ( <parameter>string</parameter> <type>text</type> <optional> <literal>FROM</literal> <parameter>start</parameter> <type>integer</type> </optional> <optional> <literal>FOR</literal> <parameter>count</parameter> <type>integer</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Extracts the substring of <parameter>string</parameter> starting at
        the <parameter>start</parameter>'th character if that is specified,
        and stopping after <parameter>count</parameter> characters if that is
        specified.  Provide at least one of <parameter>start</parameter>
        and <parameter>count</parameter>.
       </para>
       <para>
        <literal>substring('Thomas' from 2 for 3)</literal>