I'd be very interested to hear what people say about this bird.
I've twice this month seen birds like this, at Ho Chung and Tai Po Kau.
I assume this bird had clearly plain tertials.
The wingbar seems a bit thicker than on the birds I saw.
This bird does seem to have an Arctic-like bill, but I must say that didn't occur to me as a possible ID with the birds I saw - they were rounder and smaller, and though they had a similar supercilium to this (not reaching the bill) I thought they were perhaps Greenish, until I saw the Ho Chung bird had a distinct rear crown stripe, at least as strong as you ever see on a Yellow-browed.
Mike Turnbull