Add a cross-reference to precedence information to CREATE OPERATOR's

documentation.  Per suggestion from Marc Cousin.

doc/src/sgml/ref/create_operator.sgml

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-$PostgreSQL: pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.53 2010/06/22 11:36:16 rhaas Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.54 2010/07/08 16:30:13 tgl Exp $
 PostgreSQL documentation
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@@ -226,6 +226,12 @@ COMMUTATOR = OPERATOR(myschema.===) ,
    Refer to <xref linkend="xoper"> for further information.
   </para>
 
+  <para>
+   It is not possible to specify an operator's lexical precedence in
+   <command>CREATE OPERATOR</>, because the parser's precedence behavior
+   is hard-wired.  See <xref linkend="sql-precedence"> for precedence details.
+  </para>
+
   <para>
    The obsolete options <literal>SORT1</>, <literal>SORT2</>,
    <literal>LTCMP</>, and <literal>GTCMP</> were formerly used to