Genes Dev. 2017 Jan 1;31(1):6-11. doi:10.1101/gad.293837.116

Vo Ngoc L, Cassidy CJ, Huang CY, Duttke SH, Kadonaga JT.

The human initiator is a distinct and abundant element that is precisely positioned in focused core promoters.

A BBCABW motif, stricter than just YR. But 'focused core promoters' do not cover all kinds of TSSes.