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 Alt Graph+key to insert a special char.

For example, when using US international layout:

• Alt Graph+e inserts é
• Alt Graph+c inserts ©

This key is on some European keyboards. It's also on Sun Microsystem's Type 6 Keyboard.

Which character is inserted with what key is dependent on the keyboard layout. [see International Keyboard Layouts]

On Windows, the right Alt becomes Alt Graph if you set your keyboard layout to one of European layouts.

On the Mac, the ⌥ option key serve the same purpose as Alt Graph. [see Mac Keyboard Viewer and Unicode]

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's Type 6 Keyboard and usually on unix “workstation” keyboards of 1980s.

Compose Key key has a Unicode symbol ⎄. [see Unicode Keyboard Symbols ⌘ ⏎ ⌫]

Dead Key

[see French Keyboard Layout]

Dead key is a special key similar to Compose key. It is used for inputting chars with diacritic marks, such as:

• é = e with acute mark
• à = a with grave mark
• ê = e with circumflex
• ñ = n with tilde
• ü = u with diaeresis

You press the dead key first, then type a letter.

Many European language layout have both Alt Graph 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.

[see Accent Marks: Trema, Umlaut, Macron, Circumflex, and All That]

Emacs has over 1k keybinding, including a full set of keys for Alt Graph, ⎄ Compose, and dead keys. [see A Curious Look at Emacs's One Thousand Keybindings]

Which is Better Design? Alt Graph, Compose, or Dead Key?

Alt Graph and ⎄ Compose serves the same purpose. The only difference is that you need to holdAlt Graph down.

Compose is a better design, because:

• ① not holding down key is more ergonomic and more efficient. [see Ban Key Chords]
• ② key sequence allows far more possible characters. For example, Alt Graph+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.