Confusion regarding the readline module

[Siddhant]

Hi!
I am having some doubts related to the readline module. I hope someone
could clear them.
1. What exactly does the readline.get_line_buffer() function do? Does
it return whatever is the current input by the user? If yes, then can
I use it to check the current inputs of the user and base the next-
word completion against whatever the user has entered so far? There
wasn't much documentation on it, and a lot of googling couldn't help
much. :(
2. Related to the completer function, what is meant by returning the
"state"th completion for "text"? Is the completer function called
everytime (for all possible values of "state") when I press the Tab
key? When/How is it called?

Basically, I need to define a completer function, that should take
into consideration whatever the user has entered so far, and complete
the next word accordingly. The same way as a "cd /some/file" is
meaningless.