RC 10562 (#47293)
When working interactively on the computer, it is valuable to be able to undo a series of commands in order to return to a previous state. We identify contradictions and limitations in the basic concepts of undo. We introduce three types of undo functions with which we examine the characteristics of undo, explain these limitations, and determine the minimum requirements for a recovery facility. Then we discuss the implications of undo for user interfaces and suggest au.xiliary functions to display and simplify the resulting history structure and to view and recover prior states
