For some reason this took me a while to figure out back when I started on Flex but to view the Source Code for the mx Classes in the Flex IDE just hold down CTRL+move your mouse cursor on top of the class and left click on it. It will open the Class in a new Tab.

I wrote this component awhile ago which is the same one in the flexlib, except i commented alot as i went so any new devlopers can just follow it and understand what i did. there are alot of comments in there. It is 100% my code with the exception of just stealing the idea from the flexlib. Hopefully it will be of aid to people new to flex and make sure you also checkout the flexlib.

ButtonScrollCanvas