A command plug-in must define doIt() and redoIt() functions. These functions execute the command's actions.
doIt() is invoked only once, the first time the command is run. redoIt() is called every subsequent time the command is run.
doIt() should instantiate all the objects and variables your command will require, and then it should call redoIt().
redoIt() should manipulate the state of the objects used in the command. These are the manipulations that are undone in undoIt().