[R-SIG-Finance] layout options of barChart in quantmod

[风]

quantmod is a fantastic tool for R.  The only problem I could not overcome is about the layout option in barChart.
The help document only said that "layout:  if NULL bypass internal layout  ".
But how could I produce the chart as shown in http://www.quantmod.com/gallery/ ?  
What value should I set the layout to obey the previous layout settings in R?
Thanks.

Wind