[XeTeX] 'mark' and 'mkmk' features

[Will Robertson]

Hello,

On the eve of the release of fontspec 1.9, I noticed that the various  
SIL fonts contain the 'mark' and 'mkmk' OpenType features. They look  
like they need to be included in fontspec under the "diacritics"  
feature, but if so I'd like an example...

(Or are these "automatic" features and not generally de-activated,  
like 'kern'?)

Anyone know more than I?

Thanks,

Will