Optionalcaptionshown by a captioning overlay each time the effect plays
Optionalpriorityhigher cuts lower when the mixer is full; 0 when omitted
Optionalretriggerwhat a second trigger does while the first still sounds: 'restart' (the default), 'ignore', or 'layer'
A sound effect described as data and voiced by a synthesis backend instead of read from a file. mwg owns the shape the game and the mixer need (an id, a priority, what a second trigger does, a caption); whatever else a backend wants (chip, voices, curves) rides along untouched, so a retro-instrument package can carry its own
SfxDefinitionthrough unchanged.