This option can be also used as a coarse file-level mechanism
to ignore uncommitted changes in tracked files (akin to what
`.gitignore` does for untracked files).
-You should remember that an explicit 'git add' operation will
-still cause the file to be refreshed from the working tree.
Git will fail (gracefully) in case it needs to modify this file
in the index e.g. when merging in a commit;
thus, in case the assumed-untracked file is changed upstream,