DOCBOOK: SUBDOC with SGML DocBook?

I edited docbook.dcl (all of them) to SUBDOC YES but Jade 
still declines:
 declared SUBDOC, but SUBDOC NO specified in SGML declaration

What am I missing?

                                                   b.



<!DOCTYPE Book PUBLIC "-//GNOME//DTD DocBook PNG Variant V1.1//EN"[
    <!ENTITY   SubDoc       system  "marks.sgml"  SUBDOC>
]>