1. A method of auto-formatting changes to computer program source code, comprising the computer-implemented steps of: analyzing the program source code to identify formatting information; selecting a set of formatting rules for controlling an auto-formatting program to implement auto-formatting according to the identified formatting information, wherein the selected rules each specify one of a plurality of formatting options; in response to editing input from a computer user via a user interface, modifying the program source code; applying the selected set of formatting rules to control the auto-formatting program to auto-format the modified source code; and storing the auto-formatted modified source code.