+(defvar custom-local-buffer nil
+ "Non-nil, in a Customization buffer, means customize a specific buffer.
+If this variable is non-nil, it should be a buffer,
+and it means customize the local bindings of that buffer.
+This variable is a permanent local, and it normally has a local binding
+in every Customization buffer.")
+(put 'custom-local-buffer 'permanent-local t)
+