How Does CouchDB Generate _rev Strings

[Robert Sosinski]

Hello,

I just wanted to ask how CouchDB generates the string used for the
_rev.  The first part (being the number) is pretty self explanatory.
However, I have not yet figured out how the second part that looks
like a MD5 digest is created.  Would it be possible to
deterministically predict the _rev "digest" before saving the
document?

Any clarification would help.

Thanks,

-Robert