anchor.diff:  all over the place in the fixture definitions which ship with
   Afterglow; here is an introduction to how they work.
   
  -==== Color
  +==== Color Channels
   
   http://deepsymmetry.org/afterglow/doc/afterglow.channels.html#var-color[afterglow.channels/color]
   returns a channel specification for a channel that controls an
   individual color intensity (such as with an RGB LED fixture). Its two
   mandatory arguments are the channel `offset` (the channel number
   reported in the fixture manual, assuming they are numbered starting
  -with `1`), and the `color`, a keyword naming the color. The standard
  -colors `:red`, `:green`, `:blue`, and `:white` will automatically
  -participate in Afterglow's color mixing for
  -<<effects#color-effects,Color Effects>>. If your fixture has other
  -color channels, and you would like them to participate in color mixing
  -as well, pass the hue value of the color channel with the optional
  -keyword argument `:hue`. (See the discussion <<hue-mixing,above>> for
  -ways to determine the hue value of your color channel.)
  +with `1` as described <<channel-offset,above>>), and the `color`, a
  +keyword naming the color. The standard colors `:red`, `:green`,
  +`:blue`, and `:white` will automatically participate in Afterglow's
  +color mixing for <<effects#color-effects,Color Effects>>. If your
  +fixture has other color channels, and you would like them to
  +participate in color mixing as well, pass the hue value of the color
  +channel with the optional keyword argument `:hue`. (See the discussion
  +<<hue-mixing,above>> for ways to determine the hue value of your color
  +channel.)
   
   If your fixture supports two-byte color values for more precise color
   mixing, use the most-significant-byte as the `offset` value, and pass
  -the offset of least-significant byte along with the optional keyword
  +the offset of least-significant byte using the optional keyword
   argument `:fine-offset`.
   
   If you want to use a label which differs from the name of the `color`
  
positive.code: your desired label with the optional keyword argument
  `:function-label`.
  
  TODO: Finish this page.
  
  * Explain how to create function specifications in all their variations,
  with range helpers, etc., and list naming conventions established so
  far, so that new fixtures can participate when they have similar
  capabilities.
  
  ## Standard Function Types
  
  
negative.code: 
  |:offset
  
  [[channel-offset]]
  |The number that identifies the channel. Each fixture listens to one
   or more channels, and is itself configured to a partcular DMX channel
   number (DMX channels range from 1 to 512). That configuration defines
  