Jump and run along platforms (solid/jump-thru objects).
Actually I also came here for the source code of platform behavior to extend it. I know that I can get source from browser or exports but it would be simply very convenient to have it here.
We intentionally do not share the source code to plugins/behaviors, as modifying them causes really painful compatibility nightmares. It really causes more problems than it solves. You should find another way to make alterations - the Platform behavior is already highly customisable from events.