newbie with lots of newbie questions!

[White_Snake]

hello!

i been studing some basic php stuff and now im open to take the challenge to learn how does vbulletin works, so far i been checking random php files on vbulletin base files and some plugins from modifications, and i have the following questions which i havent been able to solve by myself:

• what does this->registry->options[] means/contains? i know this-> its part of classes on php, but, im not sure how does the whole thing works on vbulletin
• how does vbulletin->GPC and vbulletin->input->clean_array_gpc works? its the same as on vbulletin 3 documentation?
• i need to use "Send PM" automatically functions, i have found a vbulletin 3 article on this but, i suppose its obsolete on vb4, i have tried to find how to do this by examinating private.php on vb4 and i havent had any luck, any suggestions?
• is the $db-> fuction list is the same as vb3?

thanks in advance for your time and replies