[ms]: Add missing AT&T difference items.

...to doc/groff.texi and doc/ms.ms from tmac/groff_ms.7.man.

2 files changed, 55 insertions, 0 deletions

diff --git a/doc/groff.texi b/doc/groff.texi
index cd67b742b..d83cf93b2 100644
--- a/doc/groff.texi
+++ b/doc/groff.texi
@@ -4502,6 +4502,11 @@ The general error-handling policy of @code{groff} @file{ms} is to detect
 and report errors, rather than silently to ignore them.
 
 @item
+Tenth Edition @c possibly 9th
+Research Unix supported @code{P1} and @code{P2} macros for setting code
+examples; @code{groff} @file{ms} does not.
+
+@item
 @code{groff} @file{ms} does not work in GNU @code{troff}'s
 @acronym{AT&T} compatibility mode.  If loaded when that mode is enabled,
 it aborts processing with a diagnostic message.
@@ -4553,6 +4558,15 @@ right adjust lines, but it doesn't work''.  In @code{groff} @file{ms},
 it does.
 
 @item
+To make @code{groff} @file{ms} use the default page offset (which also
+specifies the left margin), the @code{PO} register must stay undefined
+until the first @file{ms} macro is called.
+
+This implies that @samp{\n[PO]} should not be used early in the
+document, unless it is changed also: accessing an undefined register
+automatically defines it.
+
+@item
 @code{groff} @file{ms} supports the @code{PN} register, but it is not
 necessary; you can access the page number via the usual @code{%}
 register and invoke the @code{af} request to assign a different format
diff --git a/doc/ms.ms b/doc/ms.ms
index eb33954e3..341c0451c 100644
--- a/doc/ms.ms
+++ b/doc/ms.ms
@@ -3872,6 +3872,24 @@ manual [Lesk 1978].
 .
 .
 .PP
+The error-handling policy of
+.I groff ms
+is to detect and report errors,
+rather than silently to ignore them.
+.
+.
+.PP
+Tenth Edition \" possibly 9th
+Research Unix supported
+.B P1
+and
+.B P2
+macros for setting code examples;
+.I groff ms
+does not.
+.
+.
+.PP
 .I "groff ms"
 does not work in GNU
 .I troff 's \" GNU
@@ -3882,6 +3900,11 @@ it aborts processing with a diagnostic message.
 .
 .
 .PP
+Multiple line spacing is not supported
+(use a larger vertical spacing instead).
+.
+.
+.PP
 .I "groff ms"
 uses the same header and footer defaults in both
 .CW nroff
@@ -3998,6 +4021,24 @@ it does.
 .
 .
 .PP
+To make
+.I groff ms
+use the default page offset
+(which also specifies the left margin),
+the
+.B PO
+register must stay undefined until the first
+.I ms
+macro is called.
+.
+This implies that
+.B \[rs]n[PO]
+should not be used early in the document,
+unless it is changed also:
+accessing an undefined register automatically defines it.
+.
+.
+.PP
 .I "groff ms"
 supports the
 .CW PN