What does 'git blame --before <rev> -- <file>' supposed to mean?

Hello all,

I tried to do a 'git blame' on a file and wanted to see the blame before a particular revision of that file. I initially didn't know that you could achieve that with,

    $ git blame <rev> <file>

I thought I need to pass the revision as a parameter so I tried (before looking into the documentation) the command found in the subject. It worked but to my surprise it had the same result as,

    $ git blame -- <file>

I was confused and came to know from the documentation that blame doesn't have any '--before' option. That was even more surprising. Why does blame accept an option which it doesn't identify? Shouldn't it have warned that it doesn't accept the '--before' option? I guess it should not accept it because it confuses the user a lot as the could make it hard time for him to identify the issue.

'git blame' doesn't seem to be the only command that accepts options not specified in the documentation there's 'git show' for it's company,

    $ git show --grep 'regex'

But the good thing with the above command is it behaves as expected. I suspect this should be documented, anyway.

Thoughts ?

--  Kaartic