Requirements: must

A must line states what has to be true for the action to proceed, and names the phrase spoken when it is not. The subject opens the line in lowercase (the, it, or its), which is how a requirement stays distinct from prose. One fixture exercises every form:

  on stocking it
    it must be a tool: not-a-tool
    it must be any loose-tool: already-racked
    the player must be in the Potting Bench: too-far-away
    the player must hold the secateurs: hands-empty
    the player must see the tool rack: too-dark
    the player must reach the tool rack: out-of-reach
    phrase racked
  end on

must be a/an tests kind, must be in tests place, must be any tests membership in an open condition, plain must be compares a state or value, must have/hold/wear test possession, and must see/reach test scope. Requirements are legal in on bodies and as define action lines, never in after bodies.

There is deliberately no must not. Requirements are positive; prohibitions are refusals, and the two forms sit naturally side by side:

  on sharpening it
    it must be dull: already-sharp
    refuse when the player wears the gardening mittens: mittens-on
    change it to sharp
    phrase sharpened
  end on

Writing must not … (or must be no …) is a parse error (parse.must-negative) whose fix-it points at refuse when.