When a new page is opened and contains a problem whose solution is a mathematical expression, the entry field initially contains at least one blue box. Each blue box represents a mathematical expression that forms part of the complete answer. To enter a mathematical expression one must first click on a blue box. When this is done, the cursor (or "caret") appears inside the box. The cursor marks the point at which something is entered. Material can be entered using the basic keyboard or the buttons of the keypad. Individual digits can be entered only from the keyboard. Symbols can be entered using the buttons of the keypad and, sometimes, from the keyboard as well (Fig. 4.2).