Zero Width Non-Joiner (ZWNJ)

What is ZWNJ (Zero Width Non-Joiner)?

ZWNJ stands for Zero Width Non-Joiner, encoded at U+200C. Like its counterpart ZWJ (Zero Width Joiner, U+200D), ZWNJ is an invisible formatting character with zero visual width. Where ZWJ instructs rendering engines to join or ligate adjacent characters, ZWNJ does the opposite: it prevents joining, ligature formation, or cursive connection between characters that would otherwise be combined by default.

ZWNJ is primarily used in scripts that employ cursive or ligature-forming typography — most notably Arabic, Persian (Farsi), Urdu, Devanagari, and other Brahmic scripts — as well as in general typography for ligature control in Latin script.

How ZWNJ Works in Arabic and Persian

In Arabic script, most letters connect to their neighbors in a cursive flow, changing their shape based on position. Persian (Farsi) is written in Arabic script with a few additional characters. In both languages, there are grammatical and typographic situations where a word boundary or morpheme boundary should visually break the cursive connection, even though the characters are part of the same word.

For example, the Persian word می‌رود (miravad, "goes") is written with a ZWNJ between می and رود to show that these are two morphemes — a prefix and a verb — without inserting a full space. The ZWNJ breaks the cursive connection and creates a slight visual gap (a "half-space") while keeping the word as a single typographic unit for justification and line-breaking purposes. This usage is standard and required for correct Persian typography.

How ZWNJ Works in Devanagari and Brahmic Scripts

In Devanagari (used for Hindi, Sanskrit, Marathi, Nepali), ZWNJ prevents the formation of conjunct consonants. When two consonants appear together, the Devanagari rendering system normally forms a conjunct ligature — a combined glyph. Inserting ZWNJ between them preserves both consonants in their independent (virama-terminated) forms rather than combining them.

For example: क + ् + ष normally renders as the conjunct क्ष (ksha). Inserting ZWNJ (क + ् + ZWNJ + ष) renders as क् ष — the halant form of ka followed by independent sha.

ZWNJ in Latin Typography

In Latin script, ZWNJ can prevent automatic ligature formation. High-quality typography systems (TeX, OpenType) automatically ligate character pairs like fi, fl, ff, ffi, ffl. In some contexts — such as compound words in German where the ligature would cross a morpheme boundary — the ligature is typographically incorrect. ZWNJ inserted between the two letters prevents the ligature.

ZWNJ and ZWJ Comparison

Security and Data Considerations

ZWNJ, like all invisible characters, can be used to insert hidden content into text. Two visually identical strings may differ because one contains ZWNJ characters. This matters for:

• Password comparison: A password with embedded ZWNJ is technically different from one without
• Text search: Search engines typically ignore ZWNJ for matching purposes
• Data normalization: Applications processing user input should define a policy for stripping or preserving ZWNJ

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