If multiple cases apply, the one used is listed first.
A result which changes the index is an error if the index is not empty
-and not up-to-date.
+and not up to date.
Entries marked '+' have stat information. Spaces marked '*' don't
affect the result.
left in stage 0, and there are no other entries.
A result of "no merge" is an error if the index is not empty and not
-up-to-date.
+up to date.
*empty* means that the tree must not have a directory-file conflict
with the entry.