Improve documentation/warning when --with-libxml is not used in the

installation.

doc/src/sgml/datatype.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.193 2007/04/02 15:27:02 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.194 2007/04/05 01:46:27 momjian Exp $ -->
 
  <chapter id="datatype">
   <title id="datatype-title">Data Types</title>
@@ -3202,11 +3202,13 @@ SELECT * FROM test;
     advantage over storing XML data in a <type>text</type> field is that it
     checks the input values for well-formedness, and there are support
     functions to perform type-safe operations on it; see <xref
-    linkend="functions-xml">.
+    linkend="functions-xml">.  Use of this data type requires the
+    installation to have been built with <command>configure 
+    --with-libxml</>.
    </para>
 
    <para>
-    In particular, the <type>xml</type> type can store well-formed
+    The <type>xml</type> type can store well-formed
     <quote>documents</quote>, as defined by the XML standard, as well
     as <quote>content</quote> fragments, which are defined by the
     production <literal>XMLDecl? content</literal> in the XML

doc/src/sgml/func.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.374 2007/04/02 15:27:02 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.375 2007/04/05 01:46:27 momjian Exp $ -->
 
  <chapter id="functions">
   <title>Functions and Operators</title>
@@ -7511,7 +7511,9 @@ CREATE TYPE rainbow AS ENUM ('red', 'orange', 'yellow', 'green', 'blue', 'purple
    linkend="datatype-xml"> for information about the <type>xml</type>
    type.  The function-like expressions <function>xmlparse</function>
    and <function>xmlserialize</function> for converting to and from
-   type <type>xml</type> are not repeated here.
+   type <type>xml</type> are not repeated here.  Use of many of these
+   <type>xml</type> functions requires the installation to have been built
+   with <command>configure --with-libxml</>.
   </para>
 
   <sect2>

src/backend/utils/adt/xml.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.39 2007/04/02 03:49:39 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.40 2007/04/05 01:46:27 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -112,7 +112,7 @@ XmlOptionType xmloption;
 #define NO_XML_SUPPORT() \
 	ereport(ERROR, \
 			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED), \
-			 errmsg("no XML support in this installation")))
+			 errmsg("feature not supported;  no libxml support in this installation")))
 
 
 #define _textin(str) DirectFunctionCall1(textin, CStringGetDatum(str))