treatment for a trailing newline,
    the addition of complemented bracket expressions to the things
    affected by newline-sensitive matching,
    the restrictions on parentheses and back references in lookahead/lookbehind
    constraints, and the longest/shortest-match (rather than first-match)
    matching semantics.
   </para>
   </sect3>

   <sect3 id="posix-basic-regexes">
    <title>Basic Regular Expressions</title>

   <para>
    BREs differ from EREs in several respects.
    In BREs, <literal>|</literal>, <literal>+</literal>, and <literal>?</literal>
    are ordinary characters and there is no equivalent
    for their functionality.
    The delimiters for bounds are
    <literal>\{</literal> and <literal>\}</literal>,
    with <literal>{</literal> and <literal>}</literal>
    by themselves ordinary characters.
    The parentheses for nested subexpressions are
    <literal>\(</literal> and <literal>\)</literal>,
    with <literal>(</literal> and <literal>)</literal> by themselves ordinary characters.
    <literal>^</literal> is an ordinary character except at the beginning of the
    RE or the beginning of a parenthesized subexpression,
    <literal>$</literal> is an ordinary character except at the end of the
    RE or the end of a parenthesized subexpression,
    and <literal>*</literal> is an ordinary character if it appears at the beginning
    of the RE or the beginning of a parenthesized subexpression
    (after a possible leading <literal>^</literal>).
    Finally, single-digit back references are available, and
    <literal>\&lt;</literal> and <literal>\&gt;</literal>
    are synonyms for
    <literal>[[:&lt;:]]</literal> and <literal>[[:&gt;:]]</literal>
    respectively; no other escapes are available in BREs.
   </para>
   </sect3>

<!-- end re_syntax.n man page -->

   <sect3 id="posix-vs-xquery">
   <title>Differences from SQL Standard and XQuery</title>

   <indexterm zone="posix-vs-xquery">
    <primary>LIKE_REGEX</primary>
   </indexterm>

   <indexterm zone="posix-vs-xquery">
    <primary>OCCURRENCES_REGEX</primary>
   </indexterm>

   <indexterm zone="posix-vs-xquery">
    <primary>POSITION_REGEX</primary>
   </indexterm>

   <indexterm zone="posix-vs-xquery">
    <primary>SUBSTRING_REGEX</primary>
   </indexterm>

   <indexterm zone="posix-vs-xquery">
    <primary>TRANSLATE_REGEX</primary>
   </indexterm>

   <indexterm zone="posix-vs-xquery">
    <primary>XQuery regular expressions</primary>
   </indexterm>

    <para>
     Since SQL:2008, the SQL standard includes regular expression operators
     and functions that performs pattern
     matching according to the XQuery regular expression
     standard:
     <itemizedlist>
      <listitem><para><literal>LIKE_REGEX</literal></para></listitem>
      <listitem><para><literal>OCCURRENCES_REGEX</literal></para></listitem>
      <listitem><para><literal>POSITION_REGEX</literal></para></listitem>
      <listitem><para><literal>SUBSTRING_REGEX</literal></para></listitem>
      <listitem><para><literal>TRANSLATE_REGEX</literal></para></listitem>
     </itemizedlist>
     <productname>PostgreSQL</productname> does not currently implement these
     operators and functions.  You can get approximately equivalent
     functionality in each case as shown in <xref
     linkend="functions-regexp-sql-table"/>.  (Various optional clauses on
     both sides have been omitted in this table.)
    </para>

    <table id="functions-regexp-sql-table">
     <title>Regular Expression Functions Equivalencies</title>

     <tgroup cols="2">
      <thead>
       <row>
        <entry>SQL standard</entry>
        <entry><productname>PostgreSQL</productname></entry>
       </row>
      </thead>

      <tbody>
       <row>
        <entry><literal><replaceable>string</replaceable> LIKE_REGEX <replaceable>pattern</replaceable></literal></entry>
        <entry><literal>regexp_like(<replaceable>string</replaceable>, <replaceable>pattern</replaceable>)</literal> or <literal><replaceable>string</replaceable>