Jeni's Musings

Yes, I should have investigated. There are several possibilities:

• ZERO WIDTH SPACE (U+200B)
• ZERO WIDTH NON-JOINER (U+200C)
• ZERO WIDTH JOINER (U+200D)
• WORD JOINER (U+2060)
• ZERO WIDTH NO-BREAK SPACE (U+FEFF)

In Firefox, at least in some fonts, you get funny characters with ZERO WIDTH NON-JOINER and ZERO WIDTH JOINER. In IE7, you also get funny characters when you use WORD JOINER. That leaves ZERO WIDTH SPACE or ZERO WIDTH NO-BREAK SPACE, but ZERO WIDTH NO-BREAK SPACE is deprecated since that codepoint is also used for the Byte Order Mark (BOM), so looks like ZERO WIDTH SPACE is the one to use.

To see for yourself, here are their names again, but with the spaces replaced by the respective character:

• ZERO​WIDTH​SPACE​(U+200B)
• ZERO‌WIDTH‌NON-JOINER‌(U+200C)
• ZERO‍WIDTH‍JOINER‍(U+200D)
• WORD⁠JOINER⁠(U+2060)
• ZEROWIDTHNO-BREAKSPACE(U+FEFF)