customized built-in element questions

[Mark Giffin]

I have two questions I cannot seem to find the answer to in the Custom 
Elements spec,
https://www.w3.org/TR/2016/WD-custom-elements-20160721/
1. Can I use the is= syntax for more than one customized built-in 
element, like <button is="big-button red-button">?

2. Is the is= syntax for using a customized built-in element likely to 
be deprecated sometime soon? I have heard only rumors.

Thanks,
Mark