strip function that is able to place the correlation and/or regression coefficient into the strip label.
strip.xysplom(which.given, which.panel, var.name, factor.levels,
 shingle.intervals, par.strip.text = trellis.par.get("add.text"),
 strip.names = c(TRUE, TRUE), style = 1, ...)arguments to strip.default.
more arguments to
    strip.default.
The function looks for the specific factor names
  c("corr","beta","corr.beta").  If it finds them, it goes up the
  calling sequence to locate the data for the panel.  Then it calculates
  the correlation and/of regression coefficient and inserts the
  calculated value(s) as the value for the strip label.