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Example - Emulating Compose key using chained dead keys

Installer package: KbdEditInstallerUSWithLinuxComposeKey.exe

Layout file: US With Linux Compose Key.zip

Dead key table file: LinuxComposeKeys.zip

You can use the installer package to deploy this keyboard layout without any restrictions. Free Demo version can be used to make changes and test them. To deploy a modified version, a Premium, Personal or Lite edition is needed.

Keyboards on most Unix-based systems support a special Compose key, which offers an intuitive way to enter accented and other special characters as mnemonic sequences of 2 or 3 standard characters. For example, sequence <Compose> A E produces letter Æ , <Compose> 1 4 produces fraction ¼ , <Compose> ^ T M produces trademark symbol ™ etc (the complete list is shown further below).

This method proves very intuitive and easy to learn. Even though 3 or 4 key presses are needed to produce a special character, the composition characters tend to resemble the visual appearance of the final character, which makes them easy to memorize.

Windows does not support an equivalent of Compose key out of the box, but this function is very easy to emulate using chained dead keys. This example shows one such layout, in which Compose is mapped to the rarely used Scroll Lock key.

If you primarily use the standard US English keyboard, you can use the US With Linux Compose Key.zip layout without any changes (the examples page explains how).

If you use a different layout, you will have to add the Compose dead key table to it and map the Compose dead key:

• First, you have to switch to the Dead char editor and use the Import dead char table from KLD file command to import the attached LinuxComposeKeys.zip .
• To make the Scroll Lock key available for the compose function, you should first use the low-level editor to assign a "mappable" virtual key code (eg VK_ATTN) to the "physical" Scroll Lock key (scan code 0x46), as explained in this example.
• After that, the high-level view is used to assign the 0043 C _Compose dead key to both Base and Shift positions of the VK_ATTN virtual key.

Note that Compose is the only dead character that needs to be mapped to a key in the high-level view. All other interim and final dead characters (55 of them) are produced by chaining. Furthermore, only Compose is represented by a "printable" character (C). The remaining 55 dead characters are assigned to successive numerical values (E000 - E036) from the "Private Use" area. This ensures that the "compose" dead table doesn't interfere with any pre-existing dead keys.

The above demonstrates one important feature of chained dead keys: they use high-level mappings very frugally, leaving most of the positions free for standard mappings. It is not even necessary to reserve an entire key for the Compose function: instead of Scroll Lock, Compose can also be mapped to any unused modifier + VK position in the high-level editor, e.g. AltGr+C.

Compose dead table mechanics

If you decide to further customize the composition table, you'll need to know how the Compose key works behind the scenes.

As an example, we'll use the trademark symbol ™ whose composing sequence is Compose ^ T M .

	When you press the "Compose" key, you are actually activating the "0043 C _Compose" dead character. This dead character does not produce any final characters - its transformation table consists entirely of chained dead keys. Each unique first decomposition character transforms the Compose dead key into a second-level chained dead character. E.g. character 0053 ^ chains the Compose dead key into second-level dead character "E00D  Compose ^". "E00D " is chosen arbitrarily from the non-printable "Private use" area. This character is not produced by any dead keys - it only serves as a "junction point" in the chaining sequence. If you want to create a new composition sequence starting with a character which doesn't appear in the "From" list (e.g. Z), you have to create a new dead key with a unique dead character, preferably from the E000-F8FF "Private use" area e.g. E037. You should also give it a logical and consistent name, e.g. "Compose Z". Next you have to add a new "Chained dead char" transformation pair to the "0043 C _Compose" dead char to transform Z into the newly added "E037  Compose Z". Your new "Compose Z" dead char is now ready for the addition of 2-character compositions Compose Z <char> → <special_char>.
	Sequence Compose ^ activates the second-level dead key "E00D  Compose ^". Transformation pair table for this dead key consists mostly of Latin letters transformed into "Circumflex ^" accented counterparts, e.g. a → â, plus it transforms digits, brackets and operators + = to superscript forms, e.g. 2 → ². However, it also contains two chained dead transformations, one of which transforms T into third-level dead key "E036  Compose ^T" If you want to add a new final char with a 2-char decomposition starting with ^, you simply add it as a transformation pair to the "Compose ^" dead char. Likewise, if you want to add a new 3-char decomposed character starting with ^ , and having something other than existing T or M as the second character, you have to create a new "Compose ^ <char>" chained dead character - the process is analogous to creating the "Compose Z" dead char explained above.
	Finally, the "E036  Compose ^T" dead key has only one transformation pair: M → ™ ; this is the final step in the "Compose ^TM" sequence. If you need to add a new 3-char decomposed special character starting with ^ T , you would do this by adding a new transformation pair to this dead key.

Complete composition table

The below table shows all composition sequences supported by this example (table taken from here).

The table is not exhaustive but the dead char editor, together with information from this example, is all you need to add composition sequences for missing special characters. (Eg certain Unix systems support Greek accented letters, and/or additional sequences for the existing special characters).

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