The word joiner (WJ) is a Unicode format character which is used to indicate that line breaking should not occur at its position. It does not affect the formation of ligatures or cursive joining and is ignored for the purpose of text segmentation. It is encoded since Unicode version 3.2 (released in 2002) as .
The word joiner replaces the zero-width no-break space (ZWNBSP, U+FEFF), as a usage of the no-break space of zero width. The ZWNBSP is originally and currently used as the 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.
See also
Byte order mark, which uses (ZWNBSP) character
Zero-width space
Zero-width joiner, which in scripts such as Arabic or Indic causes two characters to be shown in a connected form, even if they would otherwise not.