Controls are interactive objects that exist on screens to collect or present information. Some examples of controls are buttons, edit fields and combo boxes, each of which have their own unique features.
In order to respond to user interaction, each type of control fires unique notification messages to signal what type of interaction occurred with the control. Any control message that is fired from the screen can be detected on the On Ctrl Message event of the screen. This allows you to respond with actions at that exact moment.
Each control on a screen contains a unique identifier called a Control ID, for example CTRL_BUTTON_NEXT. This ID is used to determine exactly which control fired the notification message and which control message was fired. An example of a control message is MSGID_CLICKED.
In most cases, it is not necessary to manually interact with controls since much of the functionality is built into the available screen templates. However, sometimes further customization is required and controls offer the power and flexibility to accomplish a wide range of dynamic designs.