1 Mercurial supports several ways to specify individual revisions.

     2 

     3 A plain integer is treated as a revision number. Negative integers are

     4 treated as sequential offsets from the tip, with -1 denoting the tip,

     5 -2 denoting the revision prior to the tip, and so forth.

     6 

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

     8 identifier.

     9 

    10 A hexadecimal string less than 40 characters long is treated as a

    11 unique revision identifier and is referred to as a short-form

    12 identifier. A short-form identifier is only valid if it is the prefix

    13 of exactly one full-length identifier.

    14 

    15 Any other string is treated as a tag or branch name. A tag name is a

    16 symbolic name associated with a revision identifier. A branch name

    17 denotes the tipmost revision of that branch. Tag and branch names must

    18 not contain the ":" character.

    19 

    20 The reserved name "tip" is a special tag that always identifies the

    21 most recent revision.

    22 

    23 The reserved name "null" indicates the null revision. This is the

    24 revision of an empty repository, and the parent of revision 0.

    25 

    26 The reserved name "." indicates the working directory parent. If no

    27 working directory is checked out, it is equivalent to null. If an

    28 uncommitted merge is in progress, "." is the revision of the first

    29 parent.