Position of the characters on the keys

The picture shows the four possible positions to which a character may be associated in a key.

The number of characters that can be typed with the computer keyboard is far greater than the number of keys on the keyboard. This is made possible by the function of modifier keys which, while pressed, switch the character associated with each key, choosing it from a group of two, three or four characters. The modifiers having this function are Shift and AltGr. Pressed individually or in combination they work according to the following character selection scheme:

Modifier key pressed	selected character
none	1^st position
Maiusc	2^nd position
AltGr	3^rd position
AltGr + Maiusc	4^th position

The set of characters represented in the keyboard and their specific position in each key is also called charater mapping.

Other modifier keys are Ctrl and Alt but they are not considered here because they conventionally find use as "hot keys", i.e. keyboard shortcuts for invoking commands in programs. Pressing Ctrl and Alt simultaneously is equivalent to AltGr.