how does autopattr send commands?

Hi, I'm having trouble understanding the way in which autopattr sends its input to corresponding objects. I would imagine autopattr to direct incoming information to the first inlet of whatever object is specified. But this is not exactly the case.

For example, I am sending messages to a umenu, all of which its first inlet should understand. Sending the message "umenu 4" to autopattr correctly recalls the 4th item in umenu's item list. However, other messages such as "umenu append someitem" or "umenu clear" generate the error message "bad number." How does autopattr send its messages, and how can i get it to send exactly what I want?

In general, I find the pattr family of objects to be somewhat complicated and difficult to understand. Is there any resource anyone knows of that expands upon them a bit further than what's included in the Max documentation?