[R] helps on levelplot

[Yan Wang]

I'm a new user of levelplot, and are not familiar with the terminology 
very well. Is the bar alongside the levelplot indicating color or shade 
call "colorkey"? I have to adjust the size of its label, but couldn't 
make it so far. This is how I did:

levelplot(z~x*y, grid, at=seq(0,1,by=0.1), 
colorkey=list(labels=list(cex=2)))

But I got error message "Error in draw.colorkey(x$colorkey) : Object 
"at" not found". I tried to specify "at" in colorkey too, but it didn't 
help.

A second task I have to do is to add horizontal and vertical lines on 
the levelplots, just like the way that ablines() works for image(). 
ablines doesn't work for levelplot. Any help will be much appreciated.