[docs]: Fix content and style nits.

Discuss alignment, adjustment, and margins more carefully.  Adjustment
doesn't spread output lines to "both margins" if the indentation is
nonzero.  Describe the adjustment process explicitly.  Add emphasis
distinguishing `.ce` from `.ad c`.  Drop terms "ragged-left" and
"ragged-right" from running text (but keep their concept index entries).

1 files changed, 14 insertions, 12 deletions

diff --git a/doc/groff.texi b/doc/groff.texi
index 597188319..77a3b5af4 100644
--- a/doc/groff.texi
+++ b/doc/groff.texi
@@ -7949,9 +7949,9 @@ J.\~F.\~Ossanna wrote the original CSTR\~#54.
 @endExample
 @endDefesc
 
-By default, GNU @code{troff} fills text and adjusts it to both margins.
-Filling can be disabled via the @code{nf} request and re-enabled with
-the @code{fi} request.
+By default, GNU @code{troff} fills text and adjusts it to reach the
+output line length.  Filling can be disabled via the @code{nf} request
+and reënabled with the @code{fi} request.
 
 @DefreqList {fi, }
 @DefregListEndx {.u}
@@ -7991,22 +7991,25 @@ filling is.  @var{mode} can have one of the following values.
 @table @code
 @item b
 @itemx n
-Adjust ``normally'': to both margins.  This is the GNU @code{troff}
+Adjust ``normally'': if the output line does not occupy the distance
+between the indentation and the configured output line length, GNU
+@code{troff} stretches adjustable spaces within the line until that
+length is reached.  When the indentation is zero, this mode spreads the
+line to both the left and right margins.  This is the GNU @code{troff}
 default.
 
 @item c
 @cindex centered text (filled)
 Center filled text.  Contrast with the @code{ce} request, which centers
-text without filling it.
+text @emph{without} filling it.
 
 @item l
 @cindex ragged-right text
-Align text to the left margin, producing what is sometimes called
-ragged-right text.
+Align text to the left, without adjusting it.
 
 @item r
 @cindex ragged-left text
-Align text to the right margin, producing ragged-left text.
+Align text to the right, without adjusting it.
 @end table
 
 @var{mode} can also be a value previously stored in the @code{.j}
@@ -8061,10 +8064,9 @@ not write logic to interpret or perform arithmetic on it.
 
 @Defreq {na, }
 Disable output line adjustment.  This produces the same output as
-alignment to the left margin, but the value of the adjustment mode
-register @code{.j} is altered differently.  The adjustment mode and
-enablement status are associated with the environment
-(@pxref{Environments}).
+left-alignment, but the value of the adjustment mode register @code{.j}
+is altered differently.  The adjustment mode and enablement status are
+associated with the environment (@pxref{Environments}).
 @endDefreq
 
 @DefreqList {brp, }