Re: [PATCH] git-rev-parse.txt: Document ":path" specifier

Michael J Gruber [off-list ref] writes:

The empty treeish in ":path" means "index", not "HEAD" like in probably
every other place.

I would suggest dropping the ', not "HEAD"... place.' part from the above.
It is more confusing than useful to the readers.  

E.g. "git diff <treeish>" compares with the named tree-ish, but "git diff"
compares with the index, even though the latter obviously lacks <treeish>
and does not default to HEAD.

The rule is more like "the index is used by default for missing value, but
with an operation that does not make sense with the index, it defaults to
the HEAD", I think.