[Javascript API] How to call webservices ?

Hi.

I can't find any good documentation about how to call webservices in javascript.

I found API entries for sendRequest and AjxCallback but neither shows a code example about how to call webservices using those (if they're all that's needed).

I also found this RSS Zimlet tutorial Develop an example RSS Zimlet - Zimbra :: Wiki but it doesn't explain enough the webservice part.

Any suggestion really appreciated.