Mode (user interface)
In user interface design, a mode is a state of a system in which user input is interpreted according to a particular set of rules.
Larry Tesler defines mode as "a state of the user interface that lasts for a period of time, is not associated with any particular object, and has no role other than to place an interpretation on operator input." In his book The Humane Interface, Jef Raskin defines modality as:
"An human-machine interface is modal with respect to a given gesture when (1) the current state of the interface is not the user's locus of attention and (2) the interface will execute one among several different responses to the gesture, depending on the system's current state." (Page 42).
Accordingly, an interface is not modal as long as the user is fully aware of its current state. Raskin refers to this as locus of attention (from the Latin word locus, meaning "place" or "location"), also called heedstead in English. Typically, a user is aware of a system state if the state change was purposefully initiated by the user, or if the system gives some strong signals to notify the user of the state change in the place where interaction occurs. If the user's locus of attention changes to a different area, the state of the interface may then represent a mode since the user is no longer aware of it.