anchor.diff:  Direction assigners have a `kind` of `:direction`, and their
   `target-id` is a keyword of the form `:i68` which would represent an
   assignment to the fixture or head with ID 68. The assignment values
  -they return are either a `javax.vecmath.Vector3d`, a dynamic parameter
  -which will resolve to a `Vector3d` object, or `nil`, meaning no
  -assignment should take place.
  +they return are either a `javax.vecmath.Vector3d`, a
  +<<parameters#direction-parameters,dynamic parameter>> which will
  +resolve to a `Vector3d` object, or `nil`, meaning no assignment should
  +take place.
   
   When the assignment is resolved, the vector indicates the direction in
   the <<show_space#show-space,frame of reference of the show>> to aim
  
positive.code: Aim Assigners
  ^^^^^^^^^^^^^
  
  Aim assigners have a `kind` of `:aim`, and their
  `target-id` is a keyword of the form `:i17` which would represent an
  assignment to the fixture or head with ID 17. The assignment values
  they return are either a `javax.vecmath.Point3d`, a dynamic parameter
  which will resolve to a `Point3d` object, or `nil`, meaning no
  assignment should take place.
  
  When the assignment is resolved, the point identifies the precise
  location in the <<show_space#show-space,frame of reference of the
  
negative.code: Channel assigners have a `kind` of `:channel`, and their `target-id`
  is a keyword of the form `:u1a234` which would represent an assignment
  to universe `1`, address `234`. The assignment values they return are
  either a valid DMX data value (see next paragraph), a
  <<parameters#dynamic-parameters,dynamic parameter>> which will resolve
  to a valid DMX data value, or `nil`, meaning no assignment should take
  place.
  
  
  [[dmx-values]] The DMX data value is a number in the range `[0-256)`.
  