[asterisk-users] difference between playback and background?

[Edward de Jong]

In the dial plan language of asterisk, what is the difference between prompting the user with a Playback() command vs. a Background() command? I want in a part of my dial plan to ask the user a prompt, and wait for 4 digits to be typed in. I don't want the user to have to end the string with a pound or something, just wait 2 seconds after they stop typing. ANd I do want the prompt to be interruptible if the user is fast and knows already what to do… 

I need to do some tests on the number they entered. If i use background(), and say the prompt, and then follow with a WAIT command, how do i reference the number they just typed in? does asterisk set the ${EXTEN} variable when the user types something?

What I find maddening about the asterisk documentation is a lack of clarity on the sequence of things, and what variables get set when?