Add note clarifying that XML fragments don't accept DTDs

per complaint from Craig Ringer

diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index 59a46ad0a3ad190b5e8f913f92e6831a240be070..42907791ca9b172ff428ced87d689828ddd30978 100644 (file)
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -1,4 +1,4 @@
-
+
 
  
   Data Types
@@ -3985,6 +3985,17 @@ SET xmloption TO { DOCUMENT | CONTENT };
     The default is CONTENT, so all forms of XML
     data are allowed.
    
+
+   
+    
+     With the default XML option setting, you cannot directly cast
+     character strings to type xml if they contain a
+     document type declaration, because the definition of XML content
+     fragment does not accept them.  If you need to do that, either
+     use XMLPARSE or change the XML option.
+    
+   
+