What is a Zero Width Joiner?
The Zero Width Joiner (ZWJ, U+200D) is used to combine multiple emoji into a single visual glyph. For example: 👩 + ZWJ + 💻 = 👩💻. This is how complex emoji sequences like family emojis or profession emojis are built.
Impact on Character Count
Every ZWJ counts as one character in platforms that measure byte length. A complex emoji like 👨👩👧👦 can contain 7+ code points, including multiple ZWJ characters — counting as many characters even if it appears as one symbol.