Added many comments explaining what this file is and what it should

contain.

Define an FPI for ../../en/share/sgml/bookinfo.ent.  Explain how to add
other language specific FPIs.

share/sgml/catalog

@@ -1,2 +1,36 @@
-PUBLIC "-//FreeBSD//DTD DocBook V3.0-Based Extension//EN" "freebsd.dtd"
-PUBLIC "-//FreeBSD//ENTITIES DocBook Manual Page Entities//EN" "man-refs.ent"
+  -- ...................................................................... --
+  -- FreeBSD SGML Public Identifiers ...................................... --
+  
+  -- $Id: catalog,v 1.3 1999-05-05 20:14:34 nik Exp $
+  --
+
+  -- ...................................................................... --
+  -- Language neutral ..................................................... --
+ 
+  -- These identifiers are shared across all translations of the FreeBSD
+     documentation, even though the listed language is "EN"
+  --
+
+PUBLIC "-//FreeBSD//DTD DocBook V3.0-Based Extension//EN" 
+       "freebsd.dtd"
+
+PUBLIC "-//FreeBSD//ENTITIES DocBook Manual Page Entities//EN" 
+       "man-refs.ent"
+
+  -- ...................................................................... --
+  -- English specific ..................................................... --
+
+  -- These identifiers should only be used by English language versions of 
+     the FreeBSD Documentation.
+
+     All other translations should base their FPIs on these, but change the
+     final parameter in the FPI to represent the target language, as 
+     appropriate.  Do not change the rest of the FPI
+  --
+
+PUBLIC 	"-//FreeBSD//ENTITIES DocBook BookInfo Entities//EN" 
+	"../../en/share/sgml/bookinfo.ent"
+
+  -- A hypothetical French version of the BookInfo FPI would look like
+     "-//FreeBSD//ENTITIES DocBook BookInfo Entities//FR"
+  --