1. A method of producing an instruction set for rendering on a graphic display, the instruction set comprising a sequence of time containers to be rendered, each said time container containing at least one timed element to be displayed on the graphic display, wherein the instruction set obeys a rule prohibiting a time container from referencing the content of a different time container, said method comprising the steps of: adding an attribute to a particular time container, the attribute being associated with an event, the event comprising a target element contained within the particular time container; and providing a correspondence between the event and an effect on the display of a further said time container other than the time container immediately following the particular time container in the sequence, in a manner consistent with the rule.