[groff] 13/41: groff_char(7): Update discussion of \(rn and |.

[G. Branden Robinson]

gbranden pushed a commit to branch master
in repository groff.

commit fdc33276adc35f3ee2c3f2a6e3ded69e5af9996c
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
AuthorDate: Fri Mar 4 09:57:22 2022 +1100

    groff_char(7): Update discussion of \(rn and |.
    
    * In AT&T troff, the root en extender was unified with the overline, but
      this is not true in groff.  Explain and update glyph tables
      accordingly.
    * Describe typesetter handling of \[or] and its non-unification with the
      (vertical) bar, U+007C.
    * Note the disappearance of the broken bar form of ASCII 124 in troff.
---
 man/groff_char.7.man | 54 ++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 40 insertions(+), 14 deletions(-)

diff --git a/man/groff_char.7.man b/man/groff_char.7.man
index 0c87aa1d..9ade7c2f 100644
--- a/man/groff_char.7.man
+++ b/man/groff_char.7.man
@@ -1438,7 +1438,7 @@ _
 \[br]  \e[br]  u2502   box rule +
 \&_    \&_     u005F   underscore, low line +
 \[ul]  \e[ul]  ---     underrule +
-\[rn]  \e[rn]  u203E   radical extension, overline +
+\[rn]  \e[rn]  u203E   overline +
 \[ru]  \e[ru]  ---     baseline rule +
 \[bb]  \e[bb]  u00A6   broken bar
 \[sl]  /       u002F   slash, solidus +
@@ -1536,6 +1536,16 @@ _
 The variants of the not sign may differ in appearance or spacing
 depending on the device and font selected.
 .
+Unicode does not encode a discrete \[lq]bitwise or\[rq] sign:
+on typesetter devices,
+it is drawn shorter than the bar,
+about the same height as a capital letter.
+.
+Terminal devices unify
+.B \[rs][ba]
+and
+.BR \[rs][or] .
+.
 .TS
 l l l lx.
 Output Input   Unicode Notes
@@ -1549,7 +1559,7 @@ _
 \[st]  \e[st]  u220B   such that
 \[3d]  \e[3d]  u2234   therefore
 \[tf]  \e[tf]  u2234   therefore
-\[or]  |       u007C   bitwise or +
+\[or]  |       u007C   bar
 \[or]  \e[or]  u007C   bitwise or +
 .TE
 .
@@ -1586,19 +1596,22 @@ device and font selected.
 In AT&T
 .IR troff ,
 .B \[rs](rn
+(\[lq]root en extender\[rq])
 served as the horizontal extension of the radical
 (square root)
 sign,
-.BR \[rs](sr .
+.BR \[rs](sr ,
+and was drawn at the maximum height of the typeface's bounding box;
+this enabled the special character to double as an overline
+(see subsection \[lq]Rules and lines\[rq] above).
 .
-However,
-a contemporary font's radical sign may not ascend to a maximal drawing
-position.
+A contemporary font's radical sign might not ascend to such an extreme.
 .
+In
 .IR groff ,
 you can instead use
 .B \[rs][radicalex]
-to continue of the radical sign
+to continue the radical sign
 .BR \[rs][sr] ;
 these special characters are intended for use with regular text fonts.
 .
@@ -1677,7 +1690,7 @@ _
 \[coproduct]   \e[coproduct]   u2210   coproduct ***
 \[gr]  \e[gr]  u2207   gradient +
 \[sr]  \e[sr]  u221A   radical sign, square root +
-\[rn]  \e[rn]  u203E   radical extension, overline +
+\[rn]  \e[rn]  u203E   overline +
 \[radicalex]   \e[radicalex]   ---     radical extension
 \[sqrt]        \e[sqrt]        u221A   radical sign, square root ***
 \[sqrtex]      \e[sqrtex]      ---     radical extension ***
@@ -1839,7 +1852,7 @@ man page of the
 .
 .P
 At the time Graphic Systems delivered the C/A/T phototypesetter to AT&T,
-the ASCII character set was not considered a standard basis for a font
+the ASCII character set was not considered a standard basis for a glyph
 repertoire by traditional typographers.
 .
 In the stock Times roman,
@@ -1871,10 +1884,6 @@ We also observe that the hyphen and minus sign were 
already
 a decision whence to map an input \[lq]\-\[rq] therefore had to be
 taken.
 .
-(The Model\~37 printed ASCII decimal 124 as a broken bar,
-like Unicode U+00A6,
-but the C/A/T did not.)
-.
 .TS
 center box;
 Lf(R).
@@ -1892,7 +1901,7 @@ The special font supplied the missing ASCII and Teletype 
extended
 glyphs,
 among several others.
 .
-We observe that AT&T took the opportunity to de-unify the apostrophe
+We note that AT&T took the opportunity to de-unify the apostrophe
 and acute accent
 (a choice ISO later duplicated in its 8859 series of standards).
 .
@@ -1922,6 +1931,23 @@ Lf(I),Lf(R).
 .TE
 .
 .
+.P
+One ASCII character as rendered by the Model 37 was apparently
+abandoned.
+.
+That device printed decimal 124 (|) as a broken vertical line,
+like Unicode U+00A6.
+.
+No equivalent was available on the C/A/T;
+the box rule
+.BR \[rs][br] ,
+brace vertical extension
+.BR \[rs][bv] ,
+and \[lq]or\[rq] operator
+.BR \[rs][or] ,
+were used as appropriate to the context.
+.
+.
 .\" ====================================================================
 .SH Files
 .\" ====================================================================