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20.18.  Shallow History

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 again.

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 H.