The common segmentation done in that document is
application/vnd.hp.pcl - but you might want to think more about that;
there is no strict rule.
Better be careful when using existing types, too; for instance,
the line
langCCITT 26 image/g3fax
may get you in deep trouble, since the encapsulation for fax is
specified in a certain way in the defining document for image/g3fax,
and may be quite different elsewhere.
The registration for the other non-vnd types should probably be fleshed
out with enough info that people can tell what it's about; this concerns
text/iso6429 (this is just a control character set, I think!)
application/iso10180 (application/vnd.iso.spdl? :-)
application/dec-ln03 (did you just forget vnd.?)
Security sections are also Real Fun Stuff; if vnd.ibm-modca is the
one I vaguely remember (IBM Modifiable content for Document Content
Architecture), it was quite capable of doing really strange stuff,
including grabbing pieces out of its environment and mangling them
before printing (even though I *think* it wasn't supposed to execute them)
Have fun!
Harald A