doc: improve doc for -P '\d'

This follows up to Carlo Marcelo Arenas Belón’s email
<https://lists.gnu.org/r/grep-devel/2023-04/msg00017.html>
that proposed changing the code too.  These patches change
only the documentation since we’re so near a release.
* NEWS: Be less optimistic about the fix for -P '\d',
and warn that behavior is likely to change again.
* doc/grep.texi (grep Programs): Be less specific about -P \d
behavior, since it’s still in flux.  Warn about mismatching
Unicode versions, or disagreements about obscure constructs.

1 files changed, 5 insertions, 8 deletions

diff --git a/doc/grep.texi b/doc/grep.texi
index ce6d6dc0..ff31d5d2 100644
--- a/doc/grep.texi
+++ b/doc/grep.texi
@@ -1154,18 +1154,15 @@ For documentation, refer to @url{https://www.pcre.org/}, with these caveats:
 @samp{\d} matches only the ten ASCII digits
 (and @samp{\D} matches the complement), regardless of locale.
 Use @samp{\p@{Nd@}} to also match non-ASCII digits.
-
-When @command{grep} is built with PCRE2 10.42 and earlier,
-@samp{\d} and @samp{\D} ignore in-regexp directives like @samp{(?aD)}
-and work like @samp{[0-9]} and @samp{[^0-9]} respectively.
-However, later versions of PCRE2 likely will fix this,
-and the plan is for @command{grep} to respect those directives if possible.
+(The behavior of @samp{\d} and @samp{\D} is unspecified after
+in-regexp directives like @samp{(?aD)}.)
 
 @item
 Although PCRE tracks the syntax and semantics of Perl's regular
-expressions, the match is not always exact, partly because Perl
+expressions, the match is not always exact.  For example, Perl
 evolves and a Perl installation may predate or postdate the PCRE2
-installation on the same host.
+installation on the same host, or their Unicode versions may differ,
+or Perl and PCRE2 may disagree about an obscure construct.
 
 @item
 By default, @command{grep} applies each regexp to a line at a time,