Alt Graph Key, Compose Key, Dead Key
Alt Graph Key
The Alt Graph key, usually labeled “AltGr”. This key is a modifier key. It is for inserting special characters. Press AltGraph+key to insert a special char.
For example, when using US international layout:
- AltGraph+e inserts é
- AltGraph+c inserts ©
This key is on some European keyboards. It's also on Sun Microsystem Type 6 Keyboard .
Which character is inserted with what key is dependent on the keyboard layout.
- On Microsoft Windows, the right Alt becomes AltGraph if you set your keyboard layout to one of European language layouts. [see International Keyboard Layouts]
- On macOS, the ⌥ option is the AltGraph.
The first key of similar idea, seems to be the The Top Key of the Stanford AI Lab (SAIL) keyboard
Compose Key
The Compose Key key is also for inserting special characters. But it is used in a different way than Alt Graph key.
The Compose Key is used as a starting key of a key sequence. Press Compose Key first (and release it), then type other keys, to insert a special char. For example
- Compose ' e inserts é
- Compose O c inserts ©
The Compose Key is on Sun Microsystem Type 6 Keyboard
Compose Key key has a Unicode symbol ⎄. [see Keyboard Symbols ⌘ ↩ ⌫]
Dead Key
Dead key is a special key similar to Compose key. It is used for inputting chars with diacritic marks, such as: éàêñü.
You press the dead key first, then type a letter.
For example of keyboard with dead key, see:
Many European language layout have both AltGraph key and dead keys. See: International Keyboard Layouts .
On the Mac, ⌥ option+e is a software dead key. It adds the acute mark to any letter typed after.
Emacs has over 1k keybinding, including a full set of keys for AltGraph, Compose, and dead keys. [see A Curious Look at Emacs's One Thousand Keybindings]
Difference between Alt Graph, Compose, Dead key
They are used to insert special characters. The difference is how you press them.
- Hold down AltGraph and press another key to insert a character. For example, using US international layout, AltGraph+e inserts é.
- Press Compose, release it, press key or keys to insert a character. For example, Compose ' e for é.
- Dead key is similar to Compose key, but each limited to one specific accent mark. For example, dead´ e for é, dead¨ a for ä.
Which is Better Design: Alt Graph, Compose, Dead Key
AltGraph and Compose serves the same purpose. The only difference is that you need to holdAltGraph down.
Compose is a better design, because:
- Not holding down key is more ergonomic and more efficient. [see Ban Key Chords]
- Key sequence allows far more possible characters. For example, AltGraph+e might produce é. You have 26 letters plus some punctuation keys, a total of about 40. With Compose key sequence, you can type Compose e ' to insert é. You are using 2 keys after the compose, so you have 40×40 = 1600 possibilities. [see How Many Keyboard Shortcuts Are There]
Dead key has a special place. That is, if there are a few special characters that are used very frequently, having a dead key for them is more efficient than using Compose. For example, suppose in your language the characters é and ú and í occur frequently. If you add dedicated keys for them, that would be expensive, because keys space is limited. Using Compose, you might press Compose ' e. Using Dead key, you just press dead ' e. Of course, you will need a extra physical key on your keyboard for each possible accent mark. But, if there's just a few specific symbol that you need to input frequently, it's good to have one dedicated dead key for it.
In general, keyboard should just have a Compose key.