UnicodeASCII

UnicodeASCII is a term used to describe methods for representing Unicode text using only ASCII characters. It is not a formal encoding defined by standards bodies, but a family of conventions commonly employed to ensure compatibility with systems that handle only ASCII or to simplify textual data interchange.

Approaches fall into two broad categories: lossy transliteration and lossless encoding. Transliteration maps characters to ASCII equivalents when a close approximation exists (for example, converting ä to a). This is lossy and not reversible in all cases. Lossless methods preserve the exact Unicode data by encoding it into ASCII through escape sequences or ASCII-safe encodings such as Unicode escape sequences (for example, \u00E9 or \U000000E9), percent-encoding in URLs, or Base64 after UTF-8 encoding. In practice, many workflows mix techniques, balancing readability with the requirement to preserve information.

Common use cases include storing Unicode in ASCII-only logs, embedding Unicode in source code that must remain ASCII-only, or exchanging data with legacy systems. It is important to note that ASCII itself is a 7-bit subset of Unicode, and pure ASCII cannot represent all Unicode characters without some form of encoding or escape mechanism.

Variants and related concepts include UTF-8’s ASCII compatibility for the first 128 code points, HTML and XML numeric character references, URL percent-encoding, transliteration schemes, and domains encoded with Punycode for Internationalized Domain Names.

See also: ASCII; Unicode; UTF-8; escaping; transliteration; percent-encoding; Base64.