Revision numbers
================

   Each version of a file has a unique "revision number".  Revision
numbers look like `1.1', `1.2', `1.3.2.2' or even `1.3.2.2.4.5'.  A
revision number always has an even number of period-separated decimal
integers.  By default revision 1.1 is the first revision of a file.
Each successive revision is given a new number by increasing the
rightmost number by one.  The following figure displays a few
revisions, with newer revisions to the right.

            +-----+    +-----+    +-----+    +-----+    +-----+
            ! 1.1 !----! 1.2 !----! 1.3 !----! 1.4 !----! 1.5 !
            +-----+    +-----+    +-----+    +-----+    +-----+

   CVS is not limited to linear development.  The "revision tree" can
be split into "branches", where each branch is a self-maintained line of
development.  Changes made on one branch can easily be moved back to
the main trunk.

   Each branch has a "branch number", consisting of an odd number of
period-separated decimal integers.  The branch number is created by
appending an integer to the revision number where the corresponding
branch forked off.  Having branch numbers allows more than one branch
to be forked off from a certain revision.

   All revisions on a branch have revision numbers formed by appending
an ordinal number to the branch number.  The following figure
illustrates branching with an example.

                                           +-------------+
                Branch 1.2.2.3.2 ->        ! 1.2.2.3.2.1 !
                                         / +-------------+
                                        /
                                       /
                      +---------+    +---------+    +---------+
     Branch 1.2.2 -> _! 1.2.2.1 !----! 1.2.2.2 !----! 1.2.2.3 !
                    / +---------+    +---------+    +---------+
                   /
                  /
     +-----+    +-----+    +-----+    +-----+    +-----+
     ! 1.1 !----! 1.2 !----! 1.3 !----! 1.4 !----! 1.5 !  <- The main trunk
     +-----+    +-----+    +-----+    +-----+    +-----+
                     !
                     !
                     !   +---------+    +---------+    +---------+
     Branch 1.2.4 -> +---! 1.2.4.1 !----! 1.2.4.2 !----! 1.2.4.3 !
                         +---------+    +---------+    +---------+

   The exact details of how the branch number is constructed is not
something you normally need to be concerned about, but here is how it
works: When CVS creates a branch number it picks the first unused even
integer, starting with 2.  So when you want to create a branch from
revision 6.4 it will be numbered 6.4.2.  All branch numbers ending in a
zero (such as 6.4.0) are used internally by CVS (*note Magic branch
numbers::.).  The branch 1.1.1 has a special meaning.  *Note Tracking
sources::.