@@ -77,8 +77,16 @@ two blob objects, or changes between two files on disk.
Just in case you are doing something exotic, it should be
noted that all of the <commit> in the above description, except
-in the last two forms that use ".." notations, can be any
-<tree>.
+in the last form, that use the "\..." notation, can be any
+<tree>. For instance, if you want to make diffs against an empty
+tree, you can create a tag pointing to the empty tree:
+
+'git tag' empty $('git hash-object' -t tree /dev/null)
+
+And use it for the 'git diff', for instance, to check a working tree
+for whitespaces:
+
+'git diff' --check empty
For a more complete list of ways to spell <commit>, see
"SPECIFYING REVISIONS" section in linkgit:gitrevisions[7].