Improve documentation for sv_catpvf, to note that pattern's UTF-8ness

is taken from the SV's UTF-8ness

p4raw-id: //depot/perl@23800

1 files changed, 2 insertions, 1 deletions

diff --git a/sv.c b/sv.c
index e9e0eca865..e781904c2a 100644
--- a/sv.c
+++ b/sv.c
@@ -9008,7 +9008,8 @@ output to an SV.  If the appended data contains "wide" characters
 (including, but not limited to, SVs with a UTF-8 PV formatted with %s,
 and characters >255 formatted with %c), the original SV might get
 upgraded to UTF-8.  Handles 'get' magic, but not 'set' magic.  See
-C<sv_catpvf_mg>.
+C<sv_catpvf_mg>. If the original SV was UTF-8, the pattern should be
+valid UTF-8; if the original SV was bytes, the pattern should be too.
 
 =cut */