Some operators have a DAT docked to them that contain some python functions. These functions, called "callbacks", get called when something in the operator changes.
Examples are the Execute DATs, Timer CHOP, Replicator COMP
An Operator Family that manipulates text strings: multi-line text or tables. Multi-line text is often a python Script or GLSL Shader, but can be any multi-line text. Tables are rows and columns of cells, each containing a text string.