Suppose that figures A and B are inside a room, arguing about this very subject.
Unbeknownst to B, C (a good friend of A) is eavesdropping at the door, plotting B's assassination.
A and B both decide they've had enough of the other one's mouth, so they draw their weapons and initiate Combat. Regardless of which one wins the initiative roll, one of them gets up in the other's face, and the other remains still, and the Movement phase (for them) ends with B's back to the door…
…
LIKE SO…
…but then (regardless of whether he won or lost the initiative roll) C's Movement comes last.
Now: Can C just open the door and charge up behind B, thus gaining the +4 for a rear attack in the imminent Action phase?
Or does opening the door count as an
Action all by itself (even if C had the knob turned and ready, or somebody else threw it open for him), meaning that the door cannot be opened (Action) and passed through (Movement) in the same turn, because of the sequencing?