TITLE(overlay @@ Overlays)
USAGE(
overlay(data, fac1, fac2, use.means=true,
	print.out=true, data.order=true)
)
ARGUMENTS(
ARG(data @@ either a vector of data or a matrix.)
ARG(fac1 @@ levels of the first factor.)
ARG(fac2 @@ levels of the second factor.)
ARG(use.means @@ if LANG(true), the overlays are calculated using mean sweeps,
otherwise median sweeps are used.)
ARG(print.out @@ if LANG(false), the ANOVA table is not printed.)
ARG(data.order @@ if LANG(true), then the factor effects are ordered according
to the order the levels first appear in the vectors LANG(fac1) and LANG(fac2).
If LANG(false), the factor effects are ordered alphabetically.)
)
DESCRIPTION(
Calculates overlays for one and two-way tables.
If LANG(data) is a matrix, the overlay for a
two-way  table with one observation per cell is computed and printed,
with the rows and columns of the matrix corresponding to the levels
of the two factors.
If a vector, then if the arguments LANG(fac1) and LANG(fac2) are both present,
these are assumed to be the levels of two factors in a two-way table
with one observation per cell.
If only LANG(fac1) is present, then an overlay for comparing the groups is
printed, using the group labels in LANG(fac1).
)
