UTF-16

UTF-16 (16-bit Unicode Transformation Format) is a character encoding capable of encoding all 1,112,064 valid code points of Unicode (in fact this number of code points is dictated by the design of UTF-16). The encoding is variable-length, as code points are encoded with one or two 16-bit code units. UTF-16 arose from an earlier obsolete fixed-width 16-bit encoding, now known as UCS-2 (for 2-byte Universal Character Set), once it became clear that more than 216 (65,536) code points were needed. UTF-16 is used by systems such as the Microsoft Windows API, the Java programming language and JavaScript/ECMAScript. It is also sometimes used for plain text and word-processing data files on Microsoft Windows. It is used by SMS (the SMS standard specifies UCS-2, but almost all users actually implement UTF-16 so that emojis work). UTF-16 is the only web-encoding that is incompatible with ASCII and never gained popularity on the web, where it is declared by under 0.002% of web pages (and many of these are actually UTF-8 because of "contradictory character encoding specifications" and/or "incorrect character encoding defined"). UTF-8, by comparison, accounts for 98% of all web pages. The Web Hypertext Application Technology Working Group (WHATWG) considers UTF-8 "the mandatory encoding for all [text]" and that for security reasons browser applications should not use UTF-16. In the late 1980s, work began on developing a uniform encoding for a "Universal Character Set" (UCS) that would replace earlier language-specific encodings with one coordinated system. The goal was to include all required characters from most of the world's languages, as well as symbols from technical domains such as science, mathematics, and music. The original idea was to replace the typical 256-character encodings, which required 1 byte per character, with an encoding using 65,536 (216) values, which would require 2 bytes (16 bits) per character. Two groups worked on this in parallel, ISO/IEC JTC 1/SC 2 and the Unicode Consortium, the latter representing mostly manufacturers of computing equipment.