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AltGr Key

AltGr (also Alt Graph, Alt Graphic, Alt Graphics, Alt Grill, Alt Car, Alt Char, or Right Alt) is a modifier key found on some computer keyboards and is primarily used to type characters that are unusual for the locale of the keyboard layout, such as currency symbols and accented letters. On a typical, IBM-compatible PC keyboard, the AltGr key, when present, takes the place of the right-hand Alt key. In OS X, the Option key has functions similar to the AltGr key.

AltGr is used similarly to the Shift key: it is held down when another key is struck in order to obtain a character other than the one that the latter normally produces. AltGr and Shift can also sometimes be combined to obtain yet another character. For example, on the US-International keyboard layout, the C key can be used to insert four different characters:
AltGr_Win_Menu_Ctrl_key[1]

C → c (lower case — first level)
Shift+C → C (upper case — second level)
AltGr+C → © (copyright sign — third level)
AltGr+Shift+C → ¢ (cent sign — fourth level)

Originally, US PC keyboards (specifically, the US 101-key PC/AT keyboards) did not have an AltGr key because that was relevant to only non-US markets; they simply had "left" and "right" Alt keys.

The right Alt key is usually an equivalent of the AltGr key, as both of them share the same scancode and are indistinguishable by software. However, on some keyboards it may not be the case, or (most often on laptop keyboards) the right Alt key may be missing altogether. To allow the specific functionality of AltGr when typing non-English text on such keyboards, Windows began to allow it to be emulated by pressing the Alt key together with the Control key:

Ctrl+Alt ≈ AltGr

Therefore, it is recommended that this combination not be used as a modifier in Windows keyboard shortcuts as, depending on the keyboard layout and configuration, someone trying to type a special character with it may accidentally trigger the shortcut, or the keypresses for the shortcut may be inadvertently interpreted as the user trying to input a special character.

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