!CATEGORY Variables
  !BRIEF Category for variables

  !PARAMETER -x
    !TYPE float
    !DEFAULT 0.0
    !BRIEF First variable
  !END

  !PARAMETER -y  
    !TYPE float
    !DEFAULT 0.0
    !BRIEF Second variable
  !END

!END

!CATEGORY operator 

  !PARAMETER -op
    !TYPE string
    !BRIEF Operation to perform on x and y
    !REQUIRED yes
    !DETAIL
      The operation performed is

        x <-op> y

      So if -op is 'add' the operation is
 
        x + y
  !END

!END