Shallow History is a pseudostate (see
Section 20.11, “Pseudostate”) that can remember the
last state of its container that was active. The history
pseudostate points to its default state with a transition arrow
just like the initial pseudostate does. This transition points
to the substate that will become active when there is no
history. When the container composite state has been active
before (i.e., when there is history), the substate that was
active when the container state was exited, becomes active
When placed within a multi-level hierarchy of composite
states, the shallow history only remembers the history for
states that have the same container as the history pseudostate.
It does not restore substates deeper in the hierarchy then the
history pseudostate itself.
A shallow history is represented on the diagram as a
circle containing the letter