Alt Graph Key, Compose Key, Dead Key

What is the difference between Alt Graph key, Compose key, Dead key?

They are used to insert special characters. The difference is how you press them.

• Hold down Alt Graph and press another key to insert a character. For example, using US international layout, Alt Graph+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.

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

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 List of Emacs Default Keybinding]

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

Alt Graph and ⎄ Compose serves the same purpose. The only difference is that one is a modifier key, you need to hold it down. Compose is a better design, because:

• ① it is more ergonomic and more efficient to use. Holding down key combinations induces RSI. [see Banish 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.

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.