These are panel functions for Trellis displays useful when a grouping
  variable is specified for use within panels. The x (and
  y where appropriate) variables are plotted with different
  graphical parameters for each distinct value of the grouping variable.
panel.superpose(x, y = NULL, subscripts, groups,
                panel.groups = "panel.xyplot",
                ...,
                col, col.line, col.symbol,
                pch, cex, fill, font,
                fontface, fontfamily,
                lty, lwd, alpha,
                type = "p",
                grid = lattice.getOption("default.args")$grid,
                distribute.type = FALSE)
panel.superpose.2(..., distribute.type = TRUE)panel.superpose.plain(...,
                      col, col.line, col.symbol,
                      pch, cex, fill, font,
                      fontface, fontfamily,
                      lty, lwd, alpha)
Coordinates of the points to be displayed. Usually numeric.
The panel function to be used for each subgroup of points.  Defaults
    to panel.xyplot.
To be able to distinguish between different levels of the
    originating group inside panel.groups, it will be supplied
    two special arguments called group.number and
    group.value which will hold the numeric code and factor level
    corresponding to the current level of groups.  No special
    care needs to be taken when writing a panel.groups function
    if this feature is not used.
An integer vector of subscripts giving indices of the x and
    y values in the original data source.  See the corresponding
    entry in xyplot for details.
A grouping variable.  Different graphical parameters will be used to
    plot the subsets of observations given by each distinct value of
    groups. The default graphical parameters are obtained from
    the "superpose.symbol" and "superpose.line" settings
    using trellis.par.get wherever appropriate.
Usually a character vector specifying how each group
    should be drawn.  Formally, it is passed on to the
    panel.groups function, which must know what to do with it.
    By default, panel.groups is panel.xyplot, whose
    help page describes the admissible values.
The functions panel.superpose and panel.superpose.2
    differ only in the default value of distribute.type, which
    controls the way the type argument is interpreted.  If
    distribute.type = FALSE, then the interpretation is the same
    as for panel.xyplot for each of the unique groups.  In other
    words, if type is a vector, all the individual components are
    honoured concurrently.  If distribute.type = TRUE,
    type is replicated to be as long as the number of unique
    values in groups, and one component used for the points
    corresponding to the each different group.  Even in this case, it is
    possible to request multiple types per group, specifying type
    as a list, each component being the desired type vector for
    the corresponding group.
If distribute.type = FALSE, any occurrence of "g" in
    type causes a grid to be drawn, and all such occurrences are
    removed before type is passed on to panel.groups.
Logical flag specifying whether a background reference
    grid should be drawn.  See panel.xyplot for details.
A vector color specification. See Details.
A vector color specification. See Details.
A vector color specification. See Details.
A vector plotting character specification. See Details.
A vector size factor specification. See Details.
A vector fill color specification. See Details.
A vector color specification. See Details.
A vector color specification. See Details.
A vector color specification. See Details.
A vector alpha-transparency specification. See Details.
Extra arguments.  Passed down to panel.superpose
    from panel.superpose.2, and to panel.groups from
    panel.superpose.
logical controlling interpretation of the
    type argument.
Deepayan Sarkar Deepayan.Sarkar@R-project.org
  (panel.superpose.2 originally contributed by Neil Klepeis)
panel.superpose divides up the x (and optionally
  y) variable(s) by the unique values of
  groups[subscripts], and plots each subset with different
  graphical parameters.  The graphical parameters (col.symbol,
  pch, etc.) are usually supplied as suitable atomic vectors, but
  can also be lists.  When panel.groups is called for the
  i-th level of groups, the corresponding element of each
  graphical parameter is passed to it.  In the list form, the individual
  components can themselves be vectors.
The actual plot for each subgroup is created by the
  panel.groups function.  With the default panel.groups,
  the col argument is overridden by col.line and
  col.symbol for lines and points respectively, which default to
  the "superpose.line" and "superpose.symbol" settings.
  However, col will still be supplied as an argument to
  panel.groups functions that make use of it, with a default of
  "black".  The defaults of other graphical parameters are also
  taken from the "superpose.line" and "superpose.symbol"
  settings as appropriate.  The alpha parameter takes it default
  from the "superpose.line" setting.
panel.superpose and panel.superpose.2 differ essentially
  in how type is interpreted by default.  The default behaviour
  in panel.superpose is the opposite of that in S, which is the
  same as that of panel.superpose.2.
panel.superpose.plain is the same as panel.superpose,
  except that the default settings for the style arguments are the
  same for all groups and are taken from the default plot style.
  It is used in xyplot.ts.
Different functions when used as panel.groups gives different
  types of plots, for example panel.xyplot,
  panel.dotplot and panel.average (This can
  be used to produce interaction plots).
See Lattice for an overview of the package, and
  xyplot for common arguments (in particular, the
  discussion of the extended formula interface and the groups
  argument).