xargs.1: revise option formatting

* xargs/xargs.1:

- Migrate from comma-separated to "stacked tag" formatting for command
  options.  This is easier to read and understand when option syntax is
  complex, and eliminates the problem of the comma being misinterpreted.
  Setting the comma in bold, not roman, might have increased this risk.

  Stacking tags--without direct recourse to formatter requests--however
  requires the use of a groff man(7) extension macro, `TQ` (from groff
  1.20, 2009).  Because this page needs to be portable to non-groff
  formatters, define a page-local version after testing for its
  nonexistence using other GNU troff extensions (the `do` request and
  the `d` conditional expression operator).  (Actually, the method here
  is to test for `TQ`'s existence and then ignore the macro definition
  if the test succeeds; the token `..` terminates whichever eventuates.)

- Use the `TQ` macro to stack paragraph tags presenting synonymous
  options to xargs(1).

- Use the page-local `~~` string to put unbreakable spaces (where
  supported) between short options and their arguments.  (On the other
  hand, if a paragraph tag breaks across lines, the document likely
  requires revision.)

Discussed at:
https://lists.gnu.org/r/bug-findutils/2025-11/msg00094.html

Copyright-paperwork-exempt: Yes

xargs/xargs.1

@@ -9,6 +9,17 @@
 .  ds en \-
 .  ds ~~ \ \" backslash, space
 .\}
+.
+.do if d TQ .ig
+.\" Add supplementary paragraph tag on its own line after TP.
+.de TQ
+.  br
+.  ns
+.  \" Do not quote the argument to `TP`; the user might specify
+.  \" their own quotes for multi-word tags or to exercise AT&T troff
+.  \" quoting rules.
+.  TP \\$1\"
+..
 .SH NAME
 xargs \- build and execute command lines from standard input
 .SH SYNOPSIS
@@ -76,7 +87,9 @@ An error message is issued on standard error when this happens.
 .
 .SH OPTIONS
 .TP
-.B \-0, \-\-null
+.B \-0
+.TQ
+.B \-\-null
 Input items are terminated by a null character instead of by
 whitespace, and the quotes and backslash are not special (every
 character is taken literally).
@@ -89,7 +102,9 @@ The GNU
 option produces input suitable for this mode.
 .
 .TP
-.BI "\-a " file ", \-\-arg\-file=" file
+.BI \-a\*(~~ file
+.TQ
+.BI \-\-arg\-file= file
 Read items from
 .I file
 instead of standard input.
@@ -98,7 +113,9 @@ Otherwise, standard input is redirected from
 .IR /dev/null .
 .
 .TP
-.BI "\-\-delimiter=" delim ", \-d" " delim"
+.BI \-\-delimiter= delim
+.TQ
+.BI \-d\*(~~ delim
 Input items are terminated by the specified character.
 The specified delimiter may be a single character, a C-style character escape such
 as
@@ -121,7 +138,7 @@ design your program to use
 where this is possible.
 .
 .TP
-.BI \-E " eof-str"
+.BI \-E\*(~~ eof-str
 Set the end-of-file string to
 .IR eof-str .
 If the end-of-file
@@ -133,7 +150,13 @@ nor
 is used, no end-of-file string is used.
 .
 .TP
-.BR \-e "[\fIeof-str\fR], " "\-\-eof" [\fI=eof-str\fR]
+.\" We use font selection escape sequences here because usage of `\c` in
+.\" arguments to man(7) font macros is not portable to AT&T troff.  (The
+.\" formatter's input traps don't honor them; compare GNU troff's `it`
+.\" and `itc` requests.)
+.BR \-e [\fIeof-str\fP]
+.TQ
+.BR \-\-eof [ =\fIeof-str ]
 This option is a synonym for the
 .B \-E
 option.
@@ -151,7 +174,7 @@ nor
 is used, no end-of-file string is used.
 .
 .TP
-.BI \-I " replace-str"
+.BI \-I\*(~~ replace-str
 Replace occurrences of
 .I replace-str
 in the initial-arguments with
@@ -166,7 +189,13 @@ and
 \*(rq.
 .
 .TP
-.BR \-i "[\fIreplace-str\fR], " "\-\-replace" [\fI=replace-str\fR]
+.\" We use font selection escape sequences here because usage of `\c` in
+.\" arguments to man(7) font macros is not portable to AT&T troff.  (The
+.\" formatter's input traps don't honor them; compare GNU troff's `it`
+.\" and `itc` requests.)
+.BR \-i [\fIreplace-str\fP]
+.TQ
+.BR \-\-replace [ =\fIreplace-str ]
 This option is a synonym for
 .BI \-I replace-str
 if
@@ -185,7 +214,7 @@ option is deprecated; use
 instead.
 .
 .TP
-.BI \-L " max-lines"
+.BI \-L\*(~~ max-lines
 Use at most
 .I max-lines
 nonblank input lines per command line.
@@ -195,7 +224,13 @@ Implies
 .BR \-x .
 .
 .TP
-.BR \-l "[\fImax-lines\fR], " \-\-max-lines "[=\fImax-lines\fR]"
+.\" We use font selection escape sequences here because usage of `\c` in
+.\" arguments to man(7) font macros is not portable to AT&T troff.  (The
+.\" formatter's input traps don't honor them; compare GNU troff's `it`
+.\" and `itc` requests.)
+.BR \-l [\fImax-lines\fP]
+.TQ
+.BR \-\-max\-lines [ =\fImax-lines ]
 Synonym for the
 .B \-L
 option.
@@ -214,7 +249,9 @@ option is deprecated since the POSIX standard specifies
 instead.
 .
 .TP
-.BI \-n " max-args\fR, \fI" "\-\-max\-args" \fR=\fImax-args
+.BI \-n\*(~~ max-args
+.TQ
+.BI \-\-max\-args= max-args
 Use at most
 .I max-args
 arguments per command line.
@@ -229,7 +266,9 @@ option is given, in which case
 will exit.
 .
 .TP
-.BI \-P " max-procs\fR, \fI" \-\-max\-procs "\fR=\fImax-procs"
+.BI \-P\*(~~ max-procs
+.TQ
+.BI \-\-max\-procs= max-procs
 Run up to
 .I max-procs
 processes at a time; the default is 1.
@@ -286,7 +325,9 @@ arrange for each process to produce a separate output file (or
 otherwise use separate resources).
 .
 .TP
-.B \-o, \-\-open\-tty
+.B \-o
+.TQ
+.B \-\-open\-tty
 Reopen standard input as
 .I /dev/tty
 in the child process before executing the command.
@@ -295,7 +336,9 @@ This is useful if you want
 to run an interactive application.
 .
 .TP
-.B \-p, \-\-interactive
+.B \-p
+.TQ
+.B \-\-interactive
 Prompt the user about whether to run each command line and read a line
 from the terminal.
 Only run the command line if the response starts with `y' or `Y'.
@@ -303,7 +346,7 @@ Implies
 .BR \-t .
 .
 .TP
-.BR \-\-process\-slot\-var "=\fIname\fR"
+.BI \-\-process\-slot\-var= name
 Set the environment variable
 .I name
 to a unique value in each running child process.
@@ -311,14 +354,18 @@ Values are reused once child processes exit.
 This can be used in a rudimentary load distribution scheme, for example.
 .
 .TP
-.B \-r, \-\-no\-run\-if\-empty
+.B \-r
+.TQ
+.B \-\-no\-run\-if\-empty
 If the standard input does not contain any nonblanks, do not run the
 command.
 Normally, the command is run once even if there is no input.
 This option is a GNU extension.
 .
 .TP
-.BI \-s " max-chars\fR, \fI" \-\-max\-chars "=\fImax-chars\fR"
+.BI \-s\*(~~ max-chars
+.TQ
+.BI \-\-max\-chars= max-chars
 Use at most
 .I max-chars
 characters per command line, including the
@@ -334,7 +381,7 @@ otherwise, the default value is the maximum.
 automatically adapts to tighter constraints.
 .
 .TP
-.B "\-\-show\-limits"
+.B \-\-show\-limits
 Display the limits on the command-line length which are imposed by the
 operating system,
 .BR xargs '
@@ -350,12 +397,16 @@ if you don't want
 to do anything.
 .
 .TP
-.B \-t, \-\-verbose
+.B \-t
+.TQ
+.B \-\-verbose
 Print the command line on the standard error output before executing
 it.
 .
 .TP
-.B \-x, \-\-exit
+.B \-x
+.TQ
+.B \-\-exit
 Exit if the size (see the
 .B \-s
 option) is exceeded.