Nonalphanumeric

Nonalphanumeric describes characters that are not letters or digits. In computing and text processing, an alphanumeric character is one that is a letter (A–Z, a–z) or a decimal digit (0–9); nonalphanumeric characters fall outside that set. The concept depends on character encoding and locale, so what counts as nonalphanumeric can vary in different contexts.

In ASCII, nonalphanumeric includes punctuation marks, symbols, whitespace, and control characters. Examples are spaces, periods, commas, question marks, minus signs, underscores, parentheses, currency symbols, and many other symbols. In Unicode, the range is much broader and includes a wide array of punctuation, mathematical symbols, technical marks, and emoji. Some non-Latin letters in certain scripts may be treated as letters in locale-aware definitions, which can affect whether they are considered alphanumeric.

Common uses and considerations: nonalphanumeric characters often serve as delimiters or separators in text parsing, data formats, and programming languages. They may be allowed or disallowed by input validation and password policies. In URLs and query strings, many nonalphanumeric characters have special meanings and must be percent-encoded. In HTML and other markup, some nonalphanumeric characters are represented by entities to ensure correct rendering.

See also: alphanumeric, isalnum, regular expressions, URL encoding, character encoding.