A zero-width-non-joiner character is used for 0, and a zero-width-space character for 1. [Vedhavyas’] tool was inspired by a post by [Tom], who uses a javascript example (with online demo) to ...

Each letter in the secret message is converted to binary, then encoded in zero-width characters. A zero-width-non-joiner character is used for 0, and a zero-width-space character for 1.

Ross also published proof-of-concept code —demo here— that takes someone's username and converts it into binary code, where each 1 is a zero-width space and each 0 is a zero-width non-joiner ...