;Improve documentation of locale-specific string comparison

* doc/lispref/strings.texi (Text Comparison): Mention the Unicode
collation rules and buffer-local case-tables.

diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi
index c9612e598a30227cf13e99d603fce648a76c51de..89120575f524735fcd1ad3b93eeb76459eadf327 100644 (file)
--- a/doc/lispref/strings.texi
+++ b/doc/lispref/strings.texi
@@ -564,11 +564,19 @@ equal with respect to collation rules.  A collation rule is not only
 determined by the lexicographic order of the characters contained in
 @var{string1} and @var{string2}, but also further rules about
 relations between these characters.  Usually, it is defined by the
-@var{locale} environment Emacs is running with.
-
-For example, characters with different coding points but
-the same meaning might be considered as equal, like different grave
-accent Unicode characters:
+@var{locale} environment Emacs is running with and by the Standard C
+library against which Emacs was linked@footnote{
+For more information about collation rules and their locale
+dependencies, see @uref{https://unicode.org/reports/tr10/, The Unicode
+Collation Algorithm}.  Some Standard C libraries, such as the
+@acronym{GNU} C Library (a.k.a.@: @dfn{glibc}) implement large
+portions of the Unicode Collation Algorithm and use the associated
+locale data, Common Locale Data Repository, or @acronym{CLDR}.
+}.
+
+For example, characters with different code points but the same
+meaning, like different grave accent Unicode characters, might, in
+some locales, be considered as equal:
 
 @example
 @group
@@ -756,7 +764,8 @@ The strings are compared by the numeric values of their characters.
 For instance, @var{str1} is considered less than @var{str2} if
 its first differing character has a smaller numeric value.  If
 @var{ignore-case} is non-@code{nil}, characters are converted to
-upper-case before comparing them.  Unibyte strings are converted to
+upper-case, using the current buffer's case-table (@pxref{Case
+Tables}), before comparing them.  Unibyte strings are converted to
 multibyte for comparison (@pxref{Text Representations}), so that a
 unibyte string and its conversion to multibyte are always regarded as
 equal.