anchor.diff:  running, and its sparkles can lighten the color which would otherwise
   be present in their fixtures.
   
  -|===
  +|`:held`
  +
  +|As described <<held-flag,above>>, causes the cue's effect to run only
  +as long as the corresponding controller button or pad is held down, if
  +the controller supports that capability. Currently the web interface
  +does not, but the
  +http://deepsymmetry.org/afterglow/doc/afterglow.controllers.ableton-push.html[Ableton
  +Push mapping] does, as do mappings to generic MIDI controllers created using
  +http://deepsymmetry.org/afterglow/doc/afterglow.show.html#var-add-midi-control-to-cue-mapping[afterglow.show/add-midi-control-to-cue-mapping].
  +
  +|`:variables`
  +
  +|[[cue-variables]]Specifies a sequence of show variable bindings that
  +can be used by the cue's effect. Each variable specification is a map,
  +whose content is described in the following table. These
  +specifications are used to create any necessary new variables, and a
  +map describing all the cue variables is passed to the `effect`
  +function when the cue is triggered, so they can be used as needed when
  +creating the cue's effect.
  +
  +|===
  +
  +[cols="1a,5a", options="header"]
  +.Cue variable specification map entries
  +|===
  +|Key
  +|Purpose
  +
  +|`:key`
  +
  +|Identifies the variable that is being bound to the cue.
  +
  +|===
  +
   
   [[controlling-cues]]
   Controlling Cues
  
positive.code: killed at that point, regardless of how much longer it was planning to
  run.
  
  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. Currently, only physical
  controllers, not the web interface, honor the `:held` flag, since with
  the web interface only one cell can be clicked at a time. (This will
  be easy to change if there is demand for it.)
  
  Cues can also offer pressure sensitivity on controllers which support
  this (like the Ableton Push). For such cues, one or more variable used
  
negative.code: 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 <<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
  