Allow individual interrupts to be disabled for an activity using -=. For
instance, interrupt_rest -= message will disable the
stop-resting-for-any-silly-message behaviour (and also make stop_travel
relevant to resting).
What are the possible values for xxx and yyy in 
interrupt_xxx -= yyy?
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        If the regexes are not prefixed with < or >, > is implied. So the option

        If the regexes are not prefixed with < or >, > is implied, so the option