The codice_36 message was sent to a button when the user clicked it, and codice_37 was sent when the user released the mouse inside it to trigger its action. Similarly, HyperCard sent periodic codice_48 message, codice_49, codice_50, ... and various other messages related to navigation between different cards in a HyperCard stack, as well as user input (codice_51, codice_52, ...), and system events. As far as the scripters were concerned, there were no main event loops like in other procedural programming languages.