[XeTeX] If font under fontspec

[Gareth Hughes]

Alan Munn wrote:
> On Sep 20, 2010, at 1:30 PM, Gareth Hughes wrote:
> 
>> Dear friends,
>>
>> What is the best way to write a code that will check if a certain named
>> font, or group of fonts, is being used and implement some code if it is
>> the case? I mainly want to use this to make a few tweaks to proprietary
>> fonts, mostly kerning.
>>
> I recently asked the same question here and got a bunch of responses,
> many more than I thought my simple question would elicit:
> 
> <http://www.mail-archive.com/xetex@tug.org/msg01699.html>

Some bits of the code in that conversation are interesting, but I'm
asking for a more useful implementation that checks whether a certain
font is in use now, not just whether it might be available to XeTeX.
This is because the kerning tweaks should only be implemented when the
font that needs them is being used.

Gareth.