while, once, before, after

Every clause form takes an optional while <condition> gate, checked each time the clause would fire. After the gate, comma modifiers may follow. , once limits the clause to a single firing for the whole story, as the scarecrow's shadow moment above shows.

, before <trait> and , after <trait> order clauses when several traits answer the same verb on one entity:

define trait creaky
  phrases en-US
    hinge-creak:
      The hinges creak horribly.

  on opening it, before alarmed
    phrase hinge-creak
  end on
end trait

A cabinet composed openable, alarmed, creaky creaks first, then rings its alarm bell, regardless of the order the traits were listed in.