Added XML comment to the DTD emphasizing that this DTD is for

OpenOffice.org 1.x XML Documents and is not a DTD for any ODF
document.  See Apache OpenOffice bugzilla issue #49853.

xmloff/dtd/office.dtd

@@ -20,7 +20,17 @@
  *
  ***********************************************************-->
 
+<!-- This DTD and the entities it includes are for the
+     XML document format produced by OpenOffice.org 1.x.
 
+     This DTD is for reference from the XML prolog of documents
+     in that OpenOffice.org 1.x format.  It can be used for the
+     DTD validation of those XML documents.
+
+     This DTD is not applicable to ODF documents.  ODF support
+     began in OpenOffice.org 2.x releases.  ODF XML documents
+     have Relax NG Schemas.
+     -->
 
 <!ENTITY % dtypes-mod SYSTEM "dtypes.mod">
 %dtypes-mod;