While there are too many PS clones to count, some of which are quite poor,
trying to clone something that goes through regular modifications does require
some patience. Three questions come to mid real quick for something like
this.

Q:	Which version of Adobe PS will we clone?
	Aside from the level 1 and level 2 issues, Adobe has in the past released
	new code that incorporates modifications/upgrades/fixes just as all other
	software vendors do. The level 2 stuff may seem sound now, but I assure
	you,changes will become more frequent as their customer list begins to
	dwindle in the face of competition. This allows them to shift people to
	maintenance, as well as design efforts for level 3.

Q:	Do we duplicate the bugs, or do we make it work correctly?
	From the LaserWriter to the LaserJet 4 there have been bugs. (If I had
	a number to call at HP or Adobe, they'ld have heard from me.) Deciding
	which approach to take depends on which printer you want to emulate.

Q:	Do we follow the Red Book, or do we follow someone's implementation?
	Without a doubt, there are differences between the Red Book and Adobe's
	PS. With level 2 many issues have been refined but the Red Book does
	leave big, big holes in the implementation specific stuff. It would be
	nice it the Red Bood at least pined things down enough so that two
	different implementations of Adobe's PS don't do the exact opposite given
	an identical set of conditions.

Q:	PSCRIPT.DRV?
	Having done a lot of PS clone testing myself, the unfortunate side of
	testing is the limited number of sources for test files. The primary
	source we use is Genoa. And having characterizes their 1992 PS ATS files,
	(1300+ of them) over half are taken from PSCRIPT.DRV. It may not ideal,
	but the ATS files are what the printer vendors use. I'm sure that Adobe
	uses them too, but Adobe's output is by definition correct, even if its
	wrong.

Yes, there are some very poor clones. We've seen them here at Rastek (a sub
of Genicom which has its own clone called GeniScript). Some are poor for lack
of design, some are poor because they followed the Red Book, and some are poor
because the vendors don't know what PS is.