598002 - zwsp, zwnj, zwj affect spacing when letter-spacing is increased

Status: RESOLVED DUPLICATE of bug 253143

(Core :: Layout: Text and Fonts, defect)

Description

[j. 'mach' wust]

User-Agent:       Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:2.0b6) Gecko/20100101 Firefox/4.0b6
Build Identifier: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:2.0b6) Gecko/20100101 Firefox/4.0b6

When the letter-spacing is increased in a text that contains any of the characters ZERO zwsp (WIDTH SPACE, U+200B), zwnj (ZERO WIDTH NON-JOINER, U+200C), or zwj (ZERO WIDTH JOINER, U+200D), then these characters cause doubled letterspacing. According to the Unicode Standard (chapter 16.2), these characters should not affect text rendering at all except for their special functions. In Firefox 3.6 on Mac OS X, their behaviour used to be correct.

Reproducible: Always

Steps to Reproduce:
1. Have a page with any of zwsp, zwnj, zwj.
2. Increase letter-spacing (for instance with style="letter-spacing: 0.5em;")
3. Observe how these characters cause doubled letter-spacing.
Actual Results:  
The increased letter-spacing is doubled.

Expected Results:  
The increased letter-spacing should not be affected by these characters -- excepted, of course, their special functions. The zwj, for instance, might cause two characters to ligate, in which case there should be a ligature without any letterspacing (this actually works just fine).