What it says

Heading is the line above the clock. On a daily or weekly cut-off it can name the day the cut-off falls on: write {day} where the day goes (see Days off, and the day it ships). Link text and Link address add a button beside the clock — "Shop the sale" on a site-wide bar, say — in every placement, the bar included. Leave either empty for no button.

A screen reader hears the time once, in words — "2 days, 4 hours, 12 minutes remaining" — rather than the tiles as well, and the words are kept true as the clock runs, on a cached page too. When the timer ends they say so.