It is a constraint that prevents adding a nested ignore fragment for any one of ml. m2 or m3.

It ignores all messages other than ml m2 and m3 in the scenario being described by the interaction

The meaning is undefined because the diagram is ill-formed in the absence of n>3. which must be considered.

It allows the invocation of the operations corresponding to messages m 1. m? and m3 only when they appear in that order