There is no way that I know of to exit a sequence structure, but there are ways of accomplishing the same results. If you use case structures you can choose which segments of code you wish to implement. Thus ignoring the unwanted code in the rest of the sequence structure when a certain condition is met. Another way would be to use 2 sequence structure divided at the juncture where you wish to make the descision of whether or not to go on. The second sequence structure could then be avoided if desired. Perhaps replace the sequence structure with a state machine to allow more freedom to make descisions.
