quantified atom with other normal quantifiers (including
       <literal>{</literal><replaceable>m</replaceable><literal>,</literal><replaceable>n</replaceable><literal>}</literal>
       with <replaceable>m</replaceable> equal to <replaceable>n</replaceable>)
       is greedy (prefers longest match).
      </para>
     </listitem>
     <listitem>
      <para>
       A quantified atom with a non-greedy quantifier (including
       <literal>{</literal><replaceable>m</replaceable><literal>,</literal><replaceable>n</replaceable><literal>}?</literal>
       with <replaceable>m</replaceable> equal to <replaceable>n</replaceable>)
       is non-greedy (prefers shortest match).
      </para>
     </listitem>
     <listitem>
      <para>
       A branch &mdash; that is, an RE that has no top-level
       <literal>|</literal> operator &mdash; has the same greediness as the first
       quantified atom in it that has a greediness attribute.
      </para>
     </listitem>
     <listitem>
      <para>
       An RE consisting of two or more branches connected by the
       <literal>|</literal> operator is always greedy.
      </para>
     </listitem>
    </itemizedlist>
   </para>

   <para>
    The above rules associate greediness attributes not only with individual
    quantified atoms, but with branches and entire REs that contain quantified
    atoms.  What that means is that the matching is done in such a way that
    the branch, or whole RE, matches the longest or shortest possible
    substring <emphasis>as a whole</emphasis>.  Once the length of the entire match
    is determined, the part of it that matches any particular subexpression
    is determined on the basis of the greediness attribute of that
    subexpression, with subexpressions starting earlier in the RE taking
    priority over ones starting later.
   </para>

   <para>
    An example of what this means:
<screen>
SELECT SUBSTRING('XY1234Z', 'Y*([0-9]{1,3})');
<lineannotation>Result: </lineannotation><computeroutput>123</computeroutput>
SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput>
</screen>
    In the first case, the RE as a whole is greedy because <literal>Y*</literal>
    is greedy.  It can match beginning at the <literal>Y</literal>, and it matches
    the longest possible string starting there, i.e., <literal>Y123</literal>.
    The output is the parenthesized part of that, or <literal>123</literal>.
    In the second case, the RE as a whole is non-greedy because <literal>Y*?</literal>
    is non-greedy.  It can match beginning at the <literal>Y</literal>, and it matches
    the shortest possible string starting there, i.e., <literal>Y1</literal>.
    The subexpression <literal>[0-9]{1,3}</literal> is greedy but it cannot change
    the decision as to the overall match length; so it is forced to match
    just <literal>1</literal>.
   </para>

   <para>
    In short, when an RE contains both greedy and non-greedy subexpressions,
    the total match length is either as long as possible or as short as
    possible, according to the attribute assigned to the whole RE.  The
    attributes assigned to the subexpressions only affect how much of that
    match they are allowed to <quote>eat</quote> relative to each other.
   </para>

   <para>
    The quantifiers <literal>{1,1}</literal> and <literal>{1,1}?</literal>
    can be used to force greediness or non-greediness, respectively,
    on a subexpression or a whole RE.
    This is useful when you need the whole RE to have a greediness attribute
    different from what's deduced from its elements.  As an example,
    suppose that we are trying to separate a string containing some digits
    into the digits and the parts before and after them.  We might try to
    do that like this:
<screen>
SELECT regexp_match('abc01234xyz', '(.*)(\d+)(.*)');
<lineannotation>Result: </lineannotation><computeroutput>{abc0123,4,xyz}</computeroutput>
</screen>