anchor.diff:  add to the show. This is done so that a fresh instance of the effect
   is used each time the cue is triggered, in case the effect is complex
   and maintains its own state. The effect creation function will be
  -passed a map containing any <<user-content-cue-variables,cue-specific variable bindings>>.
  +passed a map containing any <<cue-variables,cue-specific variable bindings>>.
   
   There are a number of optional keyword parameters which can be used to
   modify the cue that is created. A summary of some features are
  
positive.code: killed at that point, regardless of how much longer it was planning to
  run.
  
  [[held-flag]]Cues can also be created which run only as long as the
  corresponding controller pad is held down (this is done by passing a
  true value with the `:held` optional keyword argument when creating
  the cue). This is often done for intense effects like strobes.
  
negative.code: |===
  
  [cols="1a,5a", options="header"]
  .[[#cue-variables]]Cue variable specification maps
  |===
  |Key
  |Purpose
  