If *--merge-order* is specified, the commit history is decomposed into a unique sequence of minimal, non-linear
epochs and maximal, linear epochs. Non-linear epochs are then linearised by sorting them into merge order, which
is described below.
Maximal, linear epochs correspond to periods of sequential development. Minimal, non-linear epochs
correspond to periods of divergent development followed by a converging merge. The theory of epochs is described
in more detail at link:http://blackcubes.dyndns.org/epoch/[http://blackcubes.dyndns.org/epoch/].
The merge order for a non-linear epoch is defined as a linearisation for which the following invariants are true:
1. if a commit P is reachable from commit N, commit P sorts after commit N in the linearised list.
2. if Pi and Pj are any two parents of a merge M (with i < j), then any commit N, such that N is reachable from Pj
but not reachable from Pi, sorts before all commits reachable from Pi.
Invariant 1 states that later commits appear before earlier commits they are derived from.
Invariant 2 states that commits unique to "later" parents in a merge, appear before all commits from "earlier" parents of
a merge.
If *--show-breaks* is specified, each item of the list is output with a 2-character prefix consisting of one of:
(|), (^), (=) followed by a space.
Commits marked with (=) represent the boundaries of minimal, non-linear epochs and correspond either to the start of a period of divergent development or to the end of such a period.
Commits marked with (|) are direct parents of commits immediately preceding the marked commit in the list.
Commits marked with (^) are not parents of the immediately preceding commit. These "breaks" represent necessary discontinuities implied by trying to represent an arbtirary DAG in a linear form.
*--show-breaks* is only valid if *--merge-order* is also specified.
