[racket] response/xexpr missing?

Hello,

I'm trying out the racket web-server. Unfortunately response/xexpr seems to be missing in the current distribution of DrRacket. 
When tryint to run the example code I always get the following error message:

	expand: unbound identifier in module in: response/xexpr

I even grep'ed the whole source code and didn't find any definition of response/xexpr.

Thanks for any help,

	Alex