anchor.diff:  level of individual DMX channel values with
   <<channel-effects,channel effects>>.
   
  -Finally, Afterglow includes some examples of how to build up
  -<<complex-effects,special-purpose effects>>, which can be fun in
  -themselves, and also serve as templates and inspiration for whole new
  -kinds of effects you create on your own.
  +As mentioned above, there are a number of ways to combine these
  +effects. If you have a group of effects that you want to start and
  +stop at the same time, you can group them into a <<scenes,scene>>. To
  +smoothly transition from one effect to another you can use a
  +<<fades,fade>>, and either side of the fade can be a scene. Or you can
  +fade to or from a <<blank-effects,blank effect>>, or sequence a whole
  +list of effects or scenes using a <<chases,chase>>.
  +
  +<<conditional-effects,Conditional effects>> and
  +<<variable-effects,variable effects>> are designed to make it easy for
  +effects to influence and interact with each other by responding to and
  +setting show variables. Finally, Afterglow includes some examples of
  +how to build up <<complex-effects,special-purpose effects>>, which can
  +be fun in themselves, and also serve as templates and inspiration for
  +whole new kinds of effects you create on your own.
   
   == Basic Effect Types
   
  
positive.code: 
  == Overview
  
  When creating an effect, you assign one or more
  <<fixture_definitions#fixture-definitions,Fixtures>> to it, and it
  will generate control values for only those fixtures. The fixture
  channels affected by the effect depend on the kind of effect it is,
  and are grouped into several primary categories. The simplest kinds of
  effects apply to a single channel per fixture, or perhaps per head, if
  the fixture has multiple independent light-emitting heads. A very
  common single-channel effect is the <<dimmer-effects,dimmer effect>>.
  
  Many effects assign <<color-effects,colors>> to lights, which often
  involves multiple channels. RGB fixtures will use three channels, one
  
negative.code:                                  (beyond/laser-color-effect laser-show c))))
  ----
  
  === Variable Effects
  
  The
  http://deepsymmetry.org/afterglow/doc/afterglow.effects.show-variable.html#var-create-for-show[variable-effect]
  