Document IS [NOT] OF, which was added in 7.3.

doc/src/sgml/func.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.365 2007/02/19 22:51:44 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.366 2007/02/20 00:25:05 momjian Exp $ -->
 
  <chapter id="functions">
   <title>Functions and Operators</title>
@@ -411,6 +411,22 @@
     <literal>IS NOT NULL</literal>, respectively, except that the input
     expression must be of Boolean type.
    </para>
+ 
+   <para>
+    <indexterm>
+     <primary>IS OF</primary>
+    </indexterm>
+    <indexterm>
+     <primary>IS NOT OF</primary>
+    </indexterm>
+    It is possible to check the data type of an expression using the
+    constructs
+<synopsis>
+<replaceable>expression</replaceable> IS OF (typename, ...)
+<replaceable>expression</replaceable> IS NOT OF (typename, ...)
+</synopsis>
+    They return a boolean value based on whether the expression's data
+    type is one of the listed data types.
   </sect1>
 
   <sect1 id="functions-math">

doc/src/sgml/syntax.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.115 2007/02/06 09:16:07 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.116 2007/02/20 00:25:05 momjian Exp $ -->
 
 <chapter id="sql-syntax">
  <title>SQL Syntax</title>
@@ -847,7 +847,8 @@ SELECT (5 !) - 6;
       <row>
        <entry><token>IS</token></entry>
        <entry></entry>
-       <entry><literal>IS TRUE</>, <literal>IS FALSE</>, <literal>IS UNKNOWN</>, <literal>IS NULL</></entry>
+       <entry><literal>IS TRUE</>, <literal>IS FALSE</>, <literal>IS
+       UNKNOWN</>, <literal>IS NULL</>, <literal>IS OF</></entry>
       </row>
 
       <row>