Clarifications in '4.1 Definitions'

In the document :
http://www.w3.org/TR/1998/REC-html40-19980424/conform.html#h-4.1

The following text is not quite clear :

"HTML user agent
...
A conforming user agent for HTML 4.0 is one that observes the mandatory
conditions ("must") set forth in this specification, including the
following points:
...
For reasons of backwards compatibility, we recommend that tools
interpreting HTML 4.0 continue to support HTML 3.2 (see [HTML32]) and
HTML 2.0 (see [RFC1866])."

The question is : must a HTML user agent support HTML 3.2 and HTML 2.0
to be conforming ?

Regards,

Robert LEGROS <rlegros@switch.be>