doc: Add more compatibility information for triggers

Louis-Claude Canon and Josh Kupershmidt

doc/src/sgml/ref/create_trigger.sgml

@@ -484,7 +484,8 @@ CREATE TRIGGER view_insert
   <para>
    The <command>CREATE TRIGGER</command> statement in
    <productname>PostgreSQL</productname> implements a subset of the
-   <acronym>SQL</> standard. The following functionality is currently missing:
+   <acronym>SQL</> standard. The following functionalities are currently
+   missing:
 
    <itemizedlist>
     <listitem>
@@ -500,6 +501,16 @@ CREATE TRIGGER view_insert
      </para>
     </listitem>
 
+    <listitem>
+     <para>
+      <productname>PostgreSQL</productname> does not allow the old and new
+      tables to be referenced in statement-level triggers, i.e., the tables
+      that contain all the old and/or new rows, which are referred to by the
+      <literal>OLD TABLE</literal> and <literal>NEW TABLE</literal> clauses in
+      the <acronym>SQL</> standard.
+     </para>
+    </listitem>
+
     <listitem>
      <para><productname>PostgreSQL</productname> only allows the execution
       of a user-defined function for the triggered action.  The standard