ZWNBSP is Unicode character ZERO WIDTH NO-BREAK SPACE also known as BOM.
The word joiner (WJ) is a format character in Unicode used to indicate that word separation should not occur at a position, when using scripts that do not use explicit spacing. It is encoded since Unicode version 3.2 (released in 2002) as U+2060 WORD JOINER (HTML · ). The word joiner does not produce any space and prohibits a line break at its position.
The word joiner replaces the zero width no-break space (ZWNBSP), a deprecated use of the Unicode character at code point U+FEFF. Character U+FEFF is intended for use as a Byte Order Mark (BOM) at the start of a file. However, if encountered elsewhere, it should, according to Unicode, be treated as a “zero width no-break space”. The deliberate use of U+FEFF for this purpose is deprecated as of Unicode 3.2, with the word joiner strongly preferred.