Never, because there is no W3C-designed standard anymore. Today they just take snapshots of the WHATWG standard every N months, slap their name on it, and call

Never, because there is no W3C-designed standard anymore. Today they just take snapshots of the WHATWG standard every N months, slap their name on it, and call that a standard. The browser vendors roll their eyes at this because they couldn't care less about the W3C and what it publishes, but they've tolerated it as long as it wasn't causing any problems. The issue here is that now the W3C seems to want to actually make a real standard of their own, and the vendors are going "No. Go away."