What is the two numbers in Mercurial changeset ID?
    $ hg heads
    changeset:   211:746a4ab8b3e3

What is `211` and `746a4ab8b3e3` respectively?

When I do `hg revert -r REV`, what should `REV` be?  `211` or `746a4ab8b3e3`, or `211:746a4ab8b3e3`?  
What is the two numbers in Mercurial changeset ID?
===

    $ hg heads
    changeset:   211:746a4ab8b3e3

What is `211` and `746a4ab8b3e3` respectively?

When I do `hg revert -r REV`, what should `REV` be?  `211` or `746a4ab8b3e3`, or `211:746a4ab8b3e3`?  