Document "diff=driver" attribute

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
index 126871756d560d64fb9ca18890d8b9e8da18e27c..d2edb9b14ae8fa0716d7139022ad4c7f61b355ed 100644 (file)
--- a/Documentation/gitattributes.txt
+++ b/Documentation/gitattributes.txt
@@ -151,8 +151,34 @@ Unspecified::
        text, it is treated as text.  Otherwise it would
        generate `Binary files differ`.
 
-Any other value set to `diff` attribute is ignored and git acts
-as if the attribute is left unspecified.
+String::
+
+       Diff is shown using the specified custom diff driver.
+       The driver program is given its input using the same
+       calling convention as used for GIT_EXTERNAL_DIFF
+       program.
+
+
+Defining a custom diff driver
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The definition of a diff driver is done in `gitconfig`, not
+`gitattributes` file, so strictly speaking this manual page is a
+wrong place to talk about it.  However...
+
+To define a custom diff driver `jcdiff`, add a section to your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
+
+----------------------------------------------------------------
+[diff "jcdiff"]
+       command = j-c-diff
+----------------------------------------------------------------
+
+When git needs to show you a diff for the path with `diff`
+attribute set to `jcdiff`, it calls the command you specified
+with the above configuration, i.e. `j-c-diff`, with 7
+parameters, just like `GIT_EXTERNAL_DIFF` program is called.
+See gitlink:git[7] for details.
 
 
 Performing a three-way merge
@@ -183,7 +209,7 @@ Unspecified::
        different merge driver to be used for paths to which the
        `merge` attribute is unspecified.
 
-Any other string value::
+String::
 
        3-way merge is performed using the specified custom
        merge driver.  The built-in 3-way merge driver can be