Document the alternative APIs for character classification.

1 files changed, 25 insertions, 0 deletions

diff --git a/doc/posix-functions/isdigit.texi b/doc/posix-functions/isdigit.texi
index 3939cd49f8..51fcc4bd53 100644
--- a/doc/posix-functions/isdigit.texi
+++ b/doc/posix-functions/isdigit.texi
@@ -13,3 +13,28 @@ Portability problems fixed by Gnulib:
 Portability problems not fixed by Gnulib:
 @itemize
 @end itemize
+
+Note: This function's behaviour depends on the locale, but does not support
+the multibyte characters that occur in strings in locales with
+@code{MB_CUR_MAX > 1} (this includes all the common UTF-8 locales).
+There are four alternative APIs:
+
+@table @code
+@item c_isdigit
+This function operates in a locale independent way and returns true only for
+ASCII characters.  It is provided by the Gnulib module @samp{c-ctype}.
+
+@item iswdigit
+This function operates in a locale dependent way, on wide characters.  In
+order to use it, you first have to convert from multibyte to wide characters,
+using the @code{mbrtowc} function.  It is provided by the Gnulib module
+@samp{wctype}.
+
+@item mb_isdigit
+This function operates in a locale dependent way, on multibyte characters.
+It is provided by the Gnulib module @samp{mbchar}.
+
+@item uc_is_digit
+This function operates in a locale independent way, on Unicode characters.
+It is provided by the Gnulib module @samp{unictype/ctype-digit}.
+@end table