There is four ways that effects can be defined in GRD. `"factor" = slope(s)` will vary the means by an amount of s for each step of the factor; `"factor" = extent(s)` will vary the means uniformly so that there is a difference of s between the first and the last factor level; `"factor" = custom(a,b,c..)` will alter each means by an amount of a for the first, b for the second, etc. Finally `"factor" = Rexpression("R code")` will apply R code to all levels of the factors, altering the base mean.
slope(s)
extent(s)
custom(...)
Rexpression(str)the size of the effect
a sequence with the sizes of the effects
R code string
These internal functions are not meant to be used in isolation in any meaningful way...