The part of an interactive system responsible for providing the user with information about the workings of the program on request. Help can be obtained in a number of ways: by typing the word ‘help’, by pressing a particular function key on the keyboard, or by using a mouse or other pointing device to select a ‘help’ item from a menu. Help can be hierarchical, where each topic has subtopics that can be explored down to an arbitrary number of levels, or context-sensitive, where the information provided is appropriate to the part of the program currently being used. Some help systems can be browsed through like a manual. A particular system may combine any or all of these methods. A good help system is a crucial feature of any nontrivial program.