[XeTeX] Hyphenation of "--" with tex-text mapping on

[Will Robertson]

On 05/11/2005, at 12pm, Jonathan Kew wrote:

> The reason it can happen is that font mappings (unlike traditional  
> TFM-based ligatures) are completely invisible to TeX's line- 
> breaking process. As far as it is concerned, the text still  
> contains two hyphens, and there's a legitimate discretionary break  
> after each of them.

Sorry to be dense, but if font mappings aren't involved with line  
breaking, how on earth does justification still work correctly? Won't  
the line break be determined based on the width of "--", which will  
later change after conversion to "–"?

Will