This paper presents evidence for a conjecture concerning the structure
of the set of braid types of periodic orbits of Smale's horseshoe map,
partially ordered by Boyland's forcing order. The braid types are
partitioned into totally ordered subsets, which are defined by parsing
the symbolic code of a periodic orbit into two segments, the prefix and the decoration: The set of braid types of orbits
with each given decoration is totally ordered, the order being given
by the unimodal order on symbol sequences. The conjecture is supported
by computer experiment, by proofs of special cases, and by intuitive
argument in terms of pruning theory.