zerowidth

Zerowidth refers to a class of Unicode characters that have no visible width when rendered. These characters are invisible in typical text displays, yet they can affect text processing, shaping, line breaking, and data encoding. They are part of the Unicode repertoire and are considered formatting or control characters rather than printable glyphs.

Common zerowidth characters include the zero width space (ZWSP, U+200B), the zero width non-joiner (ZWNJ, U+200C), and the zero width joiner (ZWJ, U+200D). The ZWSP marks potential boundaries between words without inserting a visible gap. The ZWNJ prevents ligatures from forming between adjacent characters, which is important for scripts that use contextual shaping. The ZWJ can influence the joining of characters in scripts that rely on ligatures to form connected glyphs. Another related character is the word joiner (U+2060), a zero-width non-breaking character used to prevent a line break without inserting visible space.

Applications of zerowidth characters include typographic control in complex scripts, bidirectional text processing, and subtle text encoding. They are also used in steganography and data encoding to hide information within text by varying the presence or sequence of these invisible code points. Conversely, their invisible nature can create privacy, security, and accessibility concerns, as they may be overlooked during editing, searching, or auditing, and can behave inconsistently across fonts and rendering engines.

In practice, zerowidth characters are encountered in software development, typesetting, and digital typography. Tools that scan or sanitize text often provide options to detect and remove or normalize these characters to prevent unintended formatting or leakage of hidden data.