[bug #61683] [me] either document $r and $R registers or rename them

[G. Branden Robinson]

URL:
  <https://savannah.gnu.org/bugs/?61683>

                 Summary: [me] either document $r and $R registers or rename
them
                 Project: GNU troff
            Submitted by: gbranden
            Submitted on: Thu 16 Dec 2021 12:48:15 AM UTC
                Category: Macro - me
                Severity: 2 - Minor
              Item Group: None
                  Status: Need Info
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

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Details:

me(7) is pretty consistent about exposing and documenting macro, register, and
string names that begin with a dollar sign.

The only exceptions I'm presently aware of (and I have looked) are `$r` and
`$R`.

These are alternative ratios for vertical spacing to type size that override
the (well-documented) `$v` and `$V` registers, respectively.

Here is the extent of their initialization and use in groff me(7).


  1088  .de @M                  \" --- set modes for display
  1089  .nr ?k 1
  1090  .@C 1
  1091  .@F \\n(df
  1092  .if \\n($R .@V
  1093  .vs \\n(.sp*\\n($Vu/100u
  1094  .nf
  1095  .if "\\*(|p"F" \
  1096  .       fi                      \" set fill mode if "F" parameter
  1097  .if \\n(_d=4 \
  1098  .       in 0
  1099  .if \\n(_d=3 \
  1100  \{\
  1101  .       in +\\n(biu
  1102  .       xl -\\n(biu
  1103  .\}
  1104  .if \\n(_d=1 \
  1105  .       ce 10000
  1106  ..

  1462  .\"             *** FONT AIDS ***
  1463  .
  1464  .
  1465  .de sz                  \" *** set point size and vertical spacing
  1466  .ps \\$1
  1467  .if \\n($r .@v
  1468  .vs \\n(.sp*\\n($vu/100u        \" default vs at pointsize + 20%
  1469  ..
  1470  .
  1471  .de @v                  \" --- possibly set $v from $r
  1472  .if (1i>=240u)&(1p<=\\n($r)&(\\n($r<=4p) .nr $v \\n($r00/1p
  1473  ..
  1474  .
  1475  .de @V                  \" --- possibly set $V from $R
  1476  .if (1i>=240u)&(1p<=\\n($R)&(\\n($R<=4p) .nr $V \\n($R00/1p
  1477  ..

  2067  .@R $r\"                \" ratio of vs to ps (may override $v)
  2069  .@R $R\"                \" same for displays (may override $V)


(Don't take the line numbers too literally, I'm pasting from a working tree.)

So `$r` overrides `$v` (and `$R` overrides `$V`) only if there are more than
240 basic units per inch (so, probably a typesetting device), and this ratio
variable is in the range of 1 to 4 points, inclusive.

It is not at all clear to me what these registers are for and I therefore am
not sure how to document them.

They are initialized to zero.  Only someone who knows about them from reading
the package sources or folklore would think to set them.

I therefore propose to move them to a more private part of the name space.  As
it happens, neither `_R` nor `_r` are taken.  Perhaps in groff 1.24 we can get
rid of them entirely.

Or maybe someone will be able to locate a use case.




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