Three Xi-Obama meetings: From casual to black tie?

No one would like to answer this?

My guess: black tie: moderately formal;
casual tie: casual, informal.

what does "Xi-Obama" mean?

The incumbent Chinese president-the incumbent American president.

It's using the analogy of dress, what to wear to a function. Casual is the most relaxed of all, black tie is at the opposite end of the spectrum.


In order to avoid confusion I'd avoid shorthand. The incumbent president of China's name is not readily known outside China. Three meetings between Xi and Obama would be understood immediately

Thanks.
Does "regent fit tuxedo" mean "royal/regent fit tuxedo"?

I'm not sure, but I think it's just the name of that particular style. We don't call it tuxedo in the UK, we call it a dinner jacket.

"Black tie" dress is quite formal. Very formal.

(In the UK, exceeded only by so-called "white tie".)