Lighttpd

I am a newbee to lighttpd. Just got the book of it and it seems it's the only book I can find. Here I have a basic question.

If I want to develop a module to make use of some of those plugin callbacks, such as handle_physical, handle_uri_clean, handle_uri_raw, handle_trigger, handle_response_header, handle_filter_response_content, what's the work mechanism that is behind those callbacks? That is, how are those callbacks work in lighttpd? Is the order of those callbacks defined by lighttpd? How to determine whether I should use a handler callback or write the code for certain functionality that the handler may provide with, say, for performance requirement?

Some insightful answer is really appreciated.