doc: clarify how -S works

The existing text was very vague about what exactly it means
for difference to "contain" a change. This seems to cause
confusion on the mailing list every month or two.

To fix it we:

1. use "introduce or remove an instance of" instead of
"contain"

2. point the user to gitdiffcore(7), which contains a more
complete explanation

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 813a7b11b99d51d3014f854770384ed4fc247c9f..9276faeb11aec2650393c56fe5edf2b571692dbd 100644 (file)
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -176,7 +176,10 @@ override configuration settings.
        number.
 
 -S<string>::
-       Look for differences that contain the change in <string>.
+       Look for differences that introduce or remove an instance of
+       <string>. Note that this is different than the string simply
+       appearing in diff output; see the 'pickaxe' entry in
+       linkgit:gitdiffcore[7] for more details.
 
 --pickaxe-all::
        When -S finds a change, show all the changes in that