[define_atBegin] installs a method, object, or capture block that should be invoked prior to processing each web request. At-begins are global for the server and all requests. They can be used to modify each request before it is processed, accomplishing tasks such as virtual url rewriting or authentication, etc.

If [abort] is called from within an at-begin, the request processing will terminate at that point and any result data will be returned to the client.

See also: [define_atEnd]