[XeTeX] Unicode visible space

[Jonathan Kew]

On 9 Feb 2006, at 11:47 am, Bruno Voisin wrote:

> 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.)

U+2423 would be the most appropriate. This is encoded in the Control  
Pictures block, along with visible representations for the control  
codes 0..31, etc.; it is also annotated in the Standard as "graphic  
for space".

A "modifier letter" wouldn't be a good choice, as that would tend to  
be treated as a word-forming character (by software that takes proper  
notice of character properties). I'd guess the "shelf" you found is  
probably used in some technical notation, perhaps linguistic.

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

Yes, things like this can be scarce in fonts. Of course, that was  
true with the old CM fonts as well--hence the "\tt" in plain TeX's  
definition. It's not a symbol normally used in text typesetting/ 
printing, and so most font developers, including Knuth, don't put it  
in most normal text fonts; they relegate it to special symbol  
collections.

Some of the Hiragino (CJK) fonts do include U+2423, as well as some  
of the older Apple fonts from OS 9 days, like Charcoal, Textile, and  
Sand.

I'm a bit surprised to note that it's also absent from Doulos SIL and  
Charis SIL, and will see if I can get it added there (though it'll be  
a while before the next release, as we just did one).

JK