1. A display device comprising a graphical user interface for manipulating entities by a manipulation operation, the graphical user interface comprising: a selectable interface entity upon which manipulation operations are operable; a first interface entity other than the selectable interface entity, the first interface entity being displayed before commencement of manipulation operations; and a second interface entity other than the selectable interface entity and the first interface entity, the second interface entity being displayed before commencement of manipulation operations, wherein the selectable interface entity, the first interface entity and the second interface entity are displayed at a same time in a screen view before commencement of a subject manipulation operation; upon commencement of the subject manipulation operation on the selectable interface entity, at least one of the first interface entity and the second interface entity is accentuated in its display in a manner visually distinguishing existing display of the at least one interface entity in the screen view to indicate, as a function of the subject manipulation operation, (a) a relationship thereof with respect to the selectable interface entity and (b) relationship as a valid participant of the subject manipulation operation as commenced, the accentuated at least one interface entity being visually distinguishing over displayed entities that are invalid as participants of the subject manipulation operation.