anchor.diff:  
   Aim parameters are a way to tell a group of fixtures to aim at a
   particular point in space, or track something in unison or in a
  -coordinated pattern. The basic way to create one is to call:
  +coordinated pattern. They are used with <<effects#aim-effects,Aim
  +Effects>>. The basic way to create one is to call:
   
   [source,clojure]
   ----
  
positive.code: nor right, neither up nor down, and straight towards the audience.
  `[1, 0, 0]` would be straight right, `[-1, 0, 0]` straight left, `[0,
  1, 0]` straight up, and `[0, 1, -1]` up and away from the audience at
  a 45° angle.
  
  All of these parameters, except for `frame-dynamic`, can themselves be
  dynamic parameters, such as show <<variable-parameters,variables>>
  
negative.code: every frame, or just once
  |=======================================================================
  
  Collectively, `x`, `y`, and `z` specify a three-dimensional point
  within the light show’s [[frame of reference|show-space]] telling the
  lights where to aim. When this vector is supplied to an
  <<effects#aim-effects,Aim Effect>>, it causes the attached lights to
  make the specified movement, if they are capable.
  
  If you need to convert inches to meters, which are the
  standard distance units in Afterglow, you can use
  http://deepsymmetry.org/afterglow/doc/afterglow.transform.html#var-inches[afterglow.transform/inches].
  
  All of these parameters, except for `frame-dynamic`, can themselves be
  dynamic parameters, such as show <<variable-parameters,variables>>
  (with the convenience shorthand of just passing in the keyword by which
  the show variable was stored) or <<oscillated-parameters,oscillated
  parameters>>.
  
  ## Pan Tilt Parameters
  
  A more traditional way of aiming fixtures involves setting pan and
  tilt angles. Afterglow supports this approach as well, although even
  in this case you use angles expressed in the standard show [[frame of
  reference|show-space]] regardless of how the individual fixtures are
  hung. Pan Tilt parameters are an alternate way to work with
  <<effects#direction-effects,Direction Effects>>. The basic way to create one is to
  call:
  
  [source,clojure]
  ----
  (afterglow.effects.params/build-pan-tilt-param)
  ----
  
  By itself this call would simply return a non-dynamic direction telling
  fixtures to point directly at the audience. However, you will use one or
  more of the following optional keyword parameters to get the dynamic
  angles you want:
  
  [cols=",,",options="header",]
  |=======================================================================
  |Parameter |Default |Purpose
  |`:pan` |`0` |How many degrees counter-clockwise should the light turn
  around the Y axis.
  
  |`:tilt` |`0` |How many degrees counter-clockwise should the light turn
  around the X axis.
  
  |`:frame-dynamic` |`true` |Whether the parameter should be calculated at
  every frame, or just once
  |=======================================================================
  
  The rotations requested by `pan` and `tilt` jointly identify the
  direction the light should turn away from the audience. The result of
  the parameter is a direction vector in the light show’s [[frame of
  reference|show-space]] telling the lights which direction they should
  point. When this vector is supplied to a
  <<effects#direction-effects,Direction Effect>>, it causes the attached
  lights to make the specified movement, if they are capable.
  
  Note that although internally Afterglow works with angles expressed in
  radians, the values of `pan` and `tilt` are in degrees, and are
  converted to radians for the convenience of the user who is more
  likely accustomed to working with angles expressed in degrees.
  
  All of these parameters, except for `frame-dynamic`, can themselves be
  dynamic parameters, such as show <<variable-parameters,variables>>
  