Note that all `charXXX' entity names have been removed from the font files.
They don't make sense for Unicode.

The following from the original troff manual (by Ossanna and Kernighan) is
unmapped:

  \(bs    shaded solid ball (Bell System logo, AT&T logo)

Character 0x002D has not been given a name because its Unicode name
"HYPHEN-MINUS" is so ambiguous that it's unusable for serious typographic use.

\(wp has been mapped to 0x2118, because according to unicode.org's
NamesList-3.0.0.txt, U+2118 "SCRIPT CAPITAL P" is really a Weierstrass p,
neither SCRIPT not CAPITAL.

The following line could be added; "space" is known to "devps" but are not
documented and not known to "devdvi" (actually, there is no space glyph
within the TeX system).

space	24	0	0x0020

"devps" maps \(a~ and ~ to asciitilde, which is equivalent to 0x02DC, but
this glyph is just too small.  We map them to 0x007E instead.

"devps" maps \(a^ and ^ to circumflex, which is equivalent to 0x02C6, but
this glyph is just too small.  We map them to 0x005E instead.

"devps" maps *U to Upsilon1, which is equivalent to 0x03D2.  We map it to
0x03A5 instead.

"devps" maps *W to Omega, which is equivalent to either 0x2126 or 0x03A9.
We map it to 0x03A9.

"devps" maps *D to Delta, which is equivalent to either 0x2206 or 0x0394.
We map it to 0x0394.


Using unnamed characters
------------------------

Assume you want to use a Unicode character not provided in the list, say
U+20AC. You need to do two things:

- Add a line

    ---	24	0	0x20AC

  (the second column is computed as 24 * wcwidth(0x20AC)) to the file
  R.proto, or, when groff is already installed, to the four fonts files in
  $(prefix)/share/groff/<version>/font/devutf8/.

- In your source file, use the notation \N'8364' where 8364 is the decimal
  representation of 0x20AC.