help/revisions.txt

help: move help topics from mercurial/help.py to help/*.txt

The help topics are loaded on demand so we wont hit the disk unless we
really have to.

    Mercurial supports several ways to specify individual revisions.

    A plain integer is treated as a revision number. Negative integers
    are treated as sequential offsets from the tip, with -1 denoting
    the tip, -2 denoting the revision prior to the tip, and so forth.

    A 40-digit hexadecimal string is treated as a unique revision
    identifier.

    A hexadecimal string less than 40 characters long is treated as a
    unique revision identifier and is referred to as a short-form
    identifier. A short-form identifier is only valid if it is the
    prefix of exactly one full-length identifier.

    Any other string is treated as a tag or branch name. A tag name is
    a symbolic name associated with a revision identifier. A branch
    name denotes the tipmost revision of that branch. Tag and branch
    names must not contain the ":" character.

    The reserved name "tip" is a special tag that always identifies
    the most recent revision.

    The reserved name "null" indicates the null revision. This is the
    revision of an empty repository, and the parent of revision 0.

    The reserved name "." indicates the working directory parent. If
    no working directory is checked out, it is equivalent to null. If
    an uncommitted merge is in progress, "." is the revision of the
    first parent.