[groff] 02/40: groff(7): Update list of writable predef regs.

[G. Branden Robinson]

gbranden pushed a commit to branch master
in repository groff.

commit 59ea138a93b2a9249f4cac4d080aa43e64781dfd
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
AuthorDate: Wed Dec 7 15:46:54 2022 -0600

    groff(7): Update list of writable predef regs.
    
    * Rename subsection to "Writable predefined registers", adding 2nd word.
    * Recast introduction.  Explain details of date/time registers.
    * Migrate from page-local `TPx` macro to ordinary `TP`.  Update
      indentation to 15n.
    * Recast register descriptions for clarity and consistent terminology.
---
 man/groff.7.man | 221 ++++++++++++++++++++++++++++++--------------------------
 1 file changed, 117 insertions(+), 104 deletions(-)

diff --git a/man/groff.7.man b/man/groff.7.man
index 7d2b10a71..ad86de561 100644
--- a/man/groff.7.man
+++ b/man/groff.7.man
@@ -5756,207 +5756,220 @@ zero if no magnification).
 .
 .
 .\" ====================================================================
-.SS "Writable registers"
+.SS "Writable predefined registers"
 .\" ====================================================================
 .
-The following registers can be read and written by the user.
+Several registers are predefined but also modifiable;
+some are updated upon interpretation of certain requests or escape
+sequences.
 .
-They have predefined default values,
-but can be modified to customize a document.
+Date- and time-related registers are set to the local time as determined
+by
+.MR ctime 3
+when the formatter launches.
+.
+This initialization can be overridden by
+.I \%SOURCE_DATE_EPOCH
+and
+.IR TZ ;
+see section \[lq]Environment\[rq] of
+.MR groff @MAN1EXT@ .
 .
 .
 .P
 .LS
 .
-.TPx
+.TP 15n
 .REG $$
-The process ID of
+Process ID of
 .IR @g@troff .
 .
-.TPx
+.TP
 .REG %
-Current page number.
+Page number.
 .
-.TPx
+.TP
 .REG c.
-Current input line number.
+Input line number.
 .
-.TPx
+.TP
 .REG ct
-Character type (set by width function
-.esc w ).
+Union of character types of each glyph rendered into dummy environment
+by
+.esc w .
 .
-.TPx
+.TP
 .REG dl
-Maximal width of last completed diversion.
+Width of last closed diversion.
 .
-.TPx
+.TP
 .REG dn
-Height of last completed diversion.
+Height of last closed diversion.
 .
-.TPx
+.TP
 .REG dw
-Current day of week (1\(en7).
+Day of the week (1\[en]7;
+1 is Sunday).
 .
-.TPx
+.TP
 .REG dy
-Current day of month (1\(en31).
+Day of the month (1\[en]31).
 .
-.TPx
+.TP
 .REG hours
-The number of hours past midnight.
-.
-Initialized at startup.
+Count of hours elapsed since midnight (0\[en]23).
 .
-.TPx
+.TP
 .REG hp
-Current horizontal position at input line.
+Horizontal drawing position relative to start of input line.
 .
-.TPx
+.TP
 .REG llx
-Lower left x-coordinate (in PostScript units) of a given PostScript
-image (set by
-.request .psbb ).
+Lower-left
+.I x
+coordinate
+(in PostScript units)
+of PostScript image;
+see
+.request .psbb .
 .
-.TPx
+.TP
 .REG lly
-Lower left y-coordinate (in PostScript units) of a given PostScript
-image (set by
-.request .psbb ).
+Lower-left
+.I y
+coordinate
+(in PostScript units)
+of PostScript image;
+see
+.request .psbb .
 .
-.TPx
+.TP
 .REG ln
-Output line number.
-.
+Output line number;
+see
+.request .nm .
 .
-.TPx
+.TP
 .REG lsn
-The count of leading spaces on an input line.
+Count of leading spaces on input line.
 .
-.
-.TPx
+.TP
 .REG lss
-The amount of horizontal space corresponding to the leading spaces
-on an input line.
-.
+Amount of horizontal space corresponding to leading spaces on input
+line.
 .
-.TPx
+.TP
 .REG minutes
-The number of minutes after the hour.
-.
-Initialized at startup.
+Count of minutes elapsed in the hour (0\[en]59).
 .
-.TPx
+.TP
 .REG mo
-Current month (1\(en12).
-.
+Month of the year (1\[en]12).
 .
-.TPx
+.TP
 .REG nl
-Current vertical position.
+Vertical drawing position.
 .
-.
-.TPx
+.TP
 .REG opmaxx
-.TPx
+.TP
 .REG opmaxy
-.TPx
+.TP
 .REG opminx
-.TPx
+.TP
 .REG opminy
-These four registers mark the top left and bottom right hand corners of
-a box which encompasses all written glyphs.
+These four registers mark the top left- and bottom right-hand corners of
+a rectangle encompassing all formatted output on the page.
+.
 They are reset to \-1 by
 .B \[rs]O0
 or
 .BR \[rs]O1 .
 .
-.TPx
+.TP
 .REG rsb
 As
 .register sb ,
 adding maximum glyph height to measurement.
 .
-.TPx
+.TP
 .REG rst
 As
 .register st ,
 adding maximum glyph depth to measurement.
 .
-.TPx
+.TP
 .REG sb
 Maximum displacement of text baseline below its original position
-in the argument to
+after rendering into dummy environment by
 .esc w .
 .
-.TPx
+.TP
 .REG seconds
-The number of seconds after the minute.
+Count of seconds elapsed in the minute (0\[en]60). \" not 59; see POSIX
 .
-Initialized at startup.
-.
-.TPx
+.TP
 .REG skw
-Right skip width from the center of the last glyph in the
-.esc w
-argument.
-.
+Skew of last glyph rendered into dummy environment by
+.esc w .
 .
-.TPx
+.TP
 .REG slimit
-If >0,
-sets the maximum quantity of objects on
+The maximum depth of
 .IR @g@troff 's
 internal input stack.
 .
 If \[<=]0,
 there is no limit:
-recursion can continue until program memory is exhausted.
+recursion can continue until available memory is exhausted.
 .
 The default is 1,000.
 .
-.
-.TPx
+.TP
 .REG ssc
-The amount of horizontal space (possibly negative) that should be
-added to the last glyph before a subscript (generated by width
-function
-.esc w ).
+Subscript correction of last glyph rendered into dummy environment by
+.esc w .
 .
-.TPx
+.TP
 .REG st
 Maximum displacement of text baseline above its original position
-in the argument to
+after rendering into dummy environment by
 .esc w .
 .
-.TPx
+.TP
 .REG systat
-The return value of the
+Return value of
 .I system()
-function executed by the last
-.request .sy
-request.
+function; see
+.request .sy .
 .
-.TPx
+.TP
 .REG urx
-Upper right x-coordinate (in PostScript units) of a given PostScript
-image (set by
-.request .psbb ).
+Upper-right
+.I x
+coordinate
+(in PostScript units)
+of PostScript image;
+see
+.request .psbb .
 .
-.TPx
+.TP
 .REG ury
-Upper right y-coordinate (in PostScript units) of a given PostScript
-image (set by
-.request .psbb ).
+Upper-right
+.I y
+coordinate
+(in PostScript units)
+of PostScript image;
+see
+.request .psbb .
 .
-.TPx
+.TP
 .REG year
-The current year.
+Gregorian year.
 .
-.TPx
+.TP
 .REG yr
-The current year minus 1900.
-.
+Gregorian year minus 1900.
 .LE
 .
 .