almost be considered a compose key, but use unintuitive numbers, instead of mnemonics, as the selector. Modern GUI character choosers often require a search function that is not much different than the compose sequences to locate a character quickly. Software support X Window System X header files call the Compose Key the "Multi_key". On Xorg the default Compose Key is +, (while pressing before is the "fourth keyboard level modifier", a different key). As this is rather inconvenient (especially for keyboards without an ) it is common to select a keyboard layout where another key such as the right-hand or is mapped to the compose key, this option is normally available in the settings of the desktop environment. The X keyboard driver does not allow the key used for Compose to also function as a modifier. On modern systems a vast number of compose sequences are supported. Windows On Microsoft Windows, a few programs such as PuTTY provide compose-key support. To emulate the compose key for all software, keyboard shortcut utilities are often involved. There are also a number of open-source utilities (such as WinCompose, AllChars, Compose-Keys, or Compose). Installable keyboard layouts (such as KbdEdit) are available that contain a compose key assigned to one of the keys like or . They work by using the dead-key chaining feature that is more commonly used to input letters with multiple diacritics. Such keyboard layouts can also be programmed directly in C (the language Windows drivers are written in), compiled using the free-of-charge Windows Driver Kit, and packaged using the free-of-charge Microsoft Keyboard Layout Creator 1.4, compatible up to the latest versions of the OS. macOS Although the Cocoa text input system allows entry of many alternate and accented characters natively in macOS, a true compose-key solution is not built in. At least one has been implemented using the Karabiner utility, which works with all applications, as does the use of certain keyboard layouts (e.g. "ABC – Extended") where Compose is implemented using the dead key chaining feature. ChromeOS Although ChromeOS is supplied with a larger repertoire of glyphs than most competitors, the chords needed to achieve them are not always as obvious as the Compose concept provides. Google has made available an add-on (ComposeKey) to compete in this market. DOS Under DOS, compose key support depended on the running application, or on a loadable keyboard driver. For example, Lotus 1-2-3 used