anchor.diff:  were legal and possible, and Afterglow will still be able to figure
   out and use the legal movements that the fixture is capable of.
   
  -|`:pan-half-circle`
  +|:pan-half-circle
   
   |If this fixture is a moving head capable of pan movements, this entry
    tells Afterglow the amount it needs to add to the DMX value sent on
  
positive.code: were legal and possible, and Afterglow will still be able to figure
  out and use the legal movements that the fixture is capable of.
  
  |`:tilt-half-circle`
  
  |If this fixture is a moving head capable of tilt movements, this entry
   tells Afterglow the amount it needs to add to the DMX value sent on
  
negative.code:  map. That map will include the chosen mode keyword as the value at
   this key.
  
  |:heads
  
  |If a fixture has multiple independent heads, which can be controlled
   individually, the channels which control the heads are grouped into a
  