Earlier quoted context omitted.
This blink is in a specific UI XML dialect, not HTML.
True, it has never been in an HTML standard, however it was definitely a documented part of early HTML. The blink element was in Netscape Navigator's HTML dialect in 1993/94, when early HTML was still just hitting IETF RFCs / DRAFTs, you can find blink in the Netscape HTML developer documentation from just after that era, DevEdge. It was never in NCSA Mosaic, the other big GUI browser of the era. Later on in the proc…
Blink shows that the webs often touted absolute backwards compatibility can be broken for really petty reasons.
At least these days you can easily bring back the fun:
blink {
animation: blink 1s steps(5, start) infinite;
}
@keyframes blink { to { visibility: hidden } }