anchor.diff:   map. That map will include the chosen mode keyword as the value at
    this key.
   
  -|`:heads`
  +|:heads
   
   |If a fixture has multiple independent heads, which can be controlled
    individually, the channels which control the heads are grouped into a
  
positive.code:  where the head is in space when the fiture is patched into the show.
   This is described in more detail <<head-specifications,below>>.
  
  |`:pan-center`
  
  |If this fixture is a moving head capable of pan movements, this entry
   tells afterglow the DMX value to send the fixture to pan it directly
  
negative.code: out which rotations are clockwise or counterclockwise with respect to
  different axes. Pan motions are rotations around the fixture Y axis.
  
  |:tilt-center
  
  |If this fixture is a moving head capable of tilt movements, this
   entry tells afterglow the DMX value to send the fixture to tilt it
  