[R] D(dnorm...)?

[Spencer Graves]

	  Can someone help me understand the following:

 > D(expression(dnorm(x, mean)), "mean")
[1] 0
 > sessionInfo()

R version 2.2.1, 2005-12-20, i386-pc-mingw32

attached base packages:
[1] "methods"   "stats"     "graphics"  "grDevices" "utils"     "datasets"
[7] "base"

	  By my computations, this should be something like 
((mean-x)/sd^2)*dnorm(...).

	  Thanks for your help.
	  Spencer Graves