1. In a computer system that supports a visual user interface development tool, a method of centrally managing user interface state information for the visual user interface development tool such that behavior for one or more user interface components or the visual user interface development tool itself may be defined dynamically at development time, the method comprising acts of: receiving a message generated within the visual user interface development tool; sending the message to be checked against a centralized behavior stack for one or more behaviors to use in processing the message; checking the centralized behavior stack containing currently available behaviors for processing messages to determine if a behavior is available; and if a behavior is available on the centralized behavior stack, then passing the message to the available behavior for processing.