GRAPE uses three mouse buttons. The left mouse-button is used to select things. The middle mouse-button is used to abort actions. The right mouse button is used for specific purposes or to open the configuration-menu some interactives provide (this is described in section 4.1.2).
GRAPE distinguishes between two different mouse-actions: "click" and "drag". "click" means that the mouse button is pressed and released while the mouse cursor is located within the to-be-selected control element. "drag" means that the mouse cursor is being moved while the mouse button is kept pressed.
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