Callbacks are low-level functions that provide control over the way that ART works. Each callback function must be "registered" in order to be automatically called by ART. ART_callback_register() registers ART callbacks.

Functions labeled as "Callback", when registered, are called by ART during certain events:

• When the user is about to create a new mark
• When they are going to delete a mark
• When the mouse is clicked over a mark

ART returns important data to you, and you can send data back to ART. This exchange of information determines whether or not to proceed with an operation. See the ART Component Callback Functions Reference section for specific information about the ART Component Callback Functions.