This was implemented in Bug 197958. Per https://bugs.webkit.org/show_bug.cgi?id=197958#c51: > Form submission is a complicated enough feature that > we probably want to put it in STP first and let web developers play with it.
<rdar://problem/88323870>
Old news, already done in Bug 235342. *** This bug has been marked as a duplicate of bug 235342 ***