[XeTeX] Unicode visible space

[Bruno Voisin]

To Unicode experts here: do you know what's the best Unicode  
equivalent to a visible space (the standard symbol for describing a  
space, \textvisiblespace in LaTeX parlance and \tt\char"20 in plain  
TeX parlance)?

Using xunicode.sty as a reference, the Open Box character at Unicode  
slot 2423 is used as visible space. Browsing through Apple's  
Character Palette (before I thought of using xunicode.sty, and save  
myself some time by doing so), a seemingly looking, but a bit wider,  
character is the Modified Letter Shelf at slot 02FD.

Does anyone know what's the best alternative? As I don't really  
understand the meaning of the blocks these symbols belong to, I'm  
unsure which one to pick up. (I have to admit, I wasn't looking for  
this when using XeTeX, but rather when writing a memo in Pages with  
Gill Sans as the main font.)

Sadly, among the various OS X fonts, only Lucida Grande seems to have  
either, while Apple Symbols doesn't.

Bruno Voisin