+ either "none", "untracked", "dirty" or "all", which is the default.
+ Using "none" will consider the submodule modified when it either contains
+ untracked or modified files or its HEAD differs from the commit recorded
+ in the superproject and can be used to override any settings of the
+ 'ignore' option in linkgit:git-config[1] or linkgit:gitmodules[5]. When