Compose key
Videos
A compose key is a key on a computer keyboard that indicates that the following keystrokes trigger the insertion of an alternate character, typically a precomposed character or a symbol.
The compose key on a DEC LK201 keyboard is the leftmost key on the bottom row.
The compose key and compose LED on Sun Type 5 and 5c keyboards is the second-rightmost key on the bottom row.
AltGr key
Videos
AltGr is a modifier key found on many computer keyboards. It is primarily used to type special characters and symbols that are not widely used in the territory where sold, such as foreign currency symbols, typographic marks and accented letters. On a typical Windows-compatible PC keyboard, the AltGr key, when present, takes the place of the right-hand Alt key. The key at this location will operate as AltGr if a keyboard layout using AltGr is chosen in the operating system, regardless of what is engraved on the key. In macOS, the Option key has functions similar to the AltGr key.
The AltGr key is the first key to the right of the space bar.