t ;`svn' doesn't support common args like -c or -b.
"String or list of strings specifying extra switches for svn diff under VC.
If nil, use the value of `vc-diff-switches' (or `diff-switches'),
-together with \"-x --diff-cmd=\"`diff-command' (since 'svn diff'
+together with \"-x --diff-cmd=\"`diff-command' (since `svn diff'
does not support the default \"-c\" value of `diff-switches').
If you want to force an empty list of arguments, use t."
:type '(choice (const :tag "Unspecified" nil)