SUBDOC feature

[Osamu Aoki <debian@aokiconsulting.com>]

Though debiandoc-sgml-doc states:

6. Unsupported SGML Features
----------------------------

     The `debiandoc-sgml' package does not support the SUBDOC feature of
     SGML.  Although it is possible to declare a SUBDOC entity in the
     document preamble and then refer to this entity in the document body,
     the output generated by the package's converters is very likely not as
     expected.

I seems to be able to use
    <!entity ch-markup          system "en/markup.sgml">
to include entire sub-document into a tag location.

What is SUBDOC feature? 

I just want to make sure I am not doing BAD thing.

-- 
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+  Osamu Aoki <debian@aokiconsulting.com> @ Cupertino, CA USA         +