Each of the names:
is bound to an extender function. In order to change the behavior of DrRacket, you can derive new classes from the standard classes for the frame, texts, canvases. Each extender accepts a function as input. The function it accepts must take a class as its argument and return a classes derived from that class as its result. For example:
(drracket:get/extend:extend-interactions-text (lambda (super%) (class super% (define/public (method1 x) ...) (super-new))))
extends the interactions text class with a method named method1.