User Agent Properties and EPUB

Hi folks,  

Would it be imaginable the EPUB 3 Community Group (or even the
Publishing Working Group) takes part in the User Agent Properties
discussion [1]? 

It is my understanding that it could help tremendously with user
settings (we indeed have something like that with namespaced variables
in Readium CSS and from personal experiments, it feels like it could be
a smooth solution). On a related note, it could impact personalization
as well at some point. 

Now, my concern is that some Reading Systems might not be able to set
them, especially cloud readers for instance. And Apple has partly
implemented the proposal already (for iPhone X's safe area insets). 

For various reasons, I personally feel like that to start fixing user
settings and overrides, this could be our best bet in the near future.
So it would probably be a lot better to check whether reading systems'
settings can fit in there or if we need something else ASAP. 

Jiminy 

Links:
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[1] https://github.com/w3c/csswg-drafts/issues/1693