Paragraph of placeholder attribute on input element
https://html.spec.whatwg.org/multipage/input.html#the-placeholder-attribute

If a user agent normally doesn't show this hint to the user when the control is focused, then the user agent should nonetheless show the hint for the control if it was focused as a result of the autofocus attribute, since in that case the user will not have had an

https://aomediacodec.github.io/av1-avif/#avif-mime-definition

.avif image/avif
.avifs image/avif-sequence

This is being prototyped in Chrome: https://bugs.chromium.org/p/chromium/issues/detail?id=960620

Presumably these should result in a network error. The current specification doesn't state anything and it's not tested either.

See the README for instructions on where to add tests. In the specification the "blob" case of https://fetch.spec.whatwg.org/#scheme-fetch needs updating to handle current URL’s blob URL entry being null.

Under point 6 of the list of steps to take to "ensure pre-insertion validity", as part of an attempt to implement a procedure involving the particular list of steps, I am having trouble unambiguously interpreting the following statement:

parent has an element child, child is a doctype, or child is non-null and a do

The term "forbidden host code point" is used exactly twice within this spec, and in one case it excludes U+0025 (%):

If asciiDomain contains a forbidden host code point, validation error, return failure.

If input contains a forbidden host code point excluding U+0025 (%), validation error, return failure.

I think it is easier for implementations to add to a definition rather than take