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

The following entity 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 is unusable for serious typographic
use.

\[wp] has been mapped to 0x2118, because according to Unicode 4.1's
NamesList.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 is 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.


Adding Unicode 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

    u20AC   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 \[u20AC] to access it.