Within the overlay tool, you are able to enter the class the method is in, the name of the method (i.e. “affected selector”), and the source code to be used in the method. Other fields allow a text description of the overlay, what order it should be applied in (in case some overlays must be applied before or after others), and check boxes to define whether the overlay is an HCI overlay, or “class side”. Class side overlays allow creation of whole new classes of methods. If you don’t know what that means, you definitely don’t want to attempt it.