bandwidth selection through cross validation in density estimation?

Hi,

The "density" function has a parameter that allows choosing a bandwidth 
using cross-validaton method, as described here:
*/'bw.ucv' and 'bw.bcv' implement unbiased and biased cross-validation 
respectively./**/

/*However, I didn't see any loops in the "density" function source code. 
I checked the program "bandwidths.c" and it looks to me that an 
optimization function "fmin.c" is used for bandwidth selection. "fmin.c" 
uses the Nelder-Mead search Method, and I don't think this is a cross 
validation method.  I wonder if I have missed any information. Could any 
one point to me where is the cross validaton implemented for bandwidth 
selection?

Thanks and best regards,
Hui