1. A computer program product comprising one or more computer-readable media having thereon a representation of a continuation-based runtime activity that includes: an environmental logic portion that is structured to assign a value to one or more parameters at execution time; a callback invocation portion that is structured to invoke any activity callback that 1) is available and that 2) has one or more characteristics, wherein the callback invocation portion is structured to cause the following to be performed at execution time if an activity callback is available at execution time that has the one or more characteristics: an act of instantiating the activity callback; an act of providing value(s) from at least one of the one or more parameters specifically to the activity callback, without generally defining the provided value(s) as part of the general environment of the continuation-based runtime activity; and an act of executing the instantiated activity callback such that the instantiated callback may operate using the provided value(s).