nonASCII

Non-ASCII refers to characters that are not part of the ASCII character set, which comprises the first 128 Unicode code points (0–127). These include letters with diacritics, Cyrillic, Greek, Chinese, Japanese, Korean scripts, and symbols such as currency signs and emoji. The term is often used to contrast with ASCII-only systems or data.

Historically, many extensions to ASCII existed (ISO/IEC 8859 series, Windows-1252) to support additional characters, but these encodings varied by locale and caused compatibility problems. The adoption of Unicode, and specifically UTF-8, provides a single encoding capable of representing virtually all characters used in writing systems. UTF-8 preserves ASCII compatibility and uses one to several bytes for non-ASCII code points, making it efficient for predominantly ASCII text.

Software handling non-ASCII must treat text as sequences of Unicode code points with an appropriate encoding, including correct input, storage, and transmission. Mismatched encodings can produce mojibake or data loss. In web and network contexts, proper MIME types, charset declarations, and URL encoding are important. Unicode normalization (NFC, NFD) helps ensure consistent representations of composed and decomposed characters for searching and comparing text.

Non-ASCII text enables internationalization and user interfaces in many languages, but it also introduces considerations for storage size, processing, and sorting of multilingual data.