on results in the respective property set to
    None.  Setting any of the properties results in the full_version being
    recomputed and the rest of the properties set from that.

    It also implements __str__, just returning the raw version given to the
    initializer.
    zd^((?P<epoch>\d+):)?(?P<upstream_version>[A-Za-z0-9.+:~-]+?)(-(?P<debian_revision>[A-Za-z0-9+.~]+))?$)