🚀 go-pugleaf

And the question is from Bell Labs, no less!

For every troff font there is a font description file
(readable ascii in DWB 3.1, binary in older troffs).
It contains the character name, width, descender/ascender
flag and numeric code. Because many fonts have more than
96 characters, you run out of printable ascii names for
the characters. For example, the English cuurency symbol
does not have an ascii representation, but is code number
220 in the PostScript font file. \N'220' will thus print
this symbol. (actually, \(ps does this as well in 3.1)

\X'string' merely copies string to the ditroff output
stream. It's up to the postprocessor to do something reasonable.
The SetColor example would only make sense if the PostScript
postprocessor (dpost) followed in the pipeline.

The visual representation and numeric code for all printable
PostScript characters is in the PostScript section of the
DWB 3.1 documentation. \X is in section 10.7 of the DWB 3.1
Troff User's Manual. For possible values of 'string' you
would have to read the entire Adobe PostScript Language
Reference Manual.