`doctype-first` does not account for comments being permitted beforehand.

[RokeJulianLockhart]

Demonstration

Explanation

The DOCTYPE declaration may be preceded by comments, after the BOM. ¹

Documents must consist of the following parts, in the given order:

1. Optionally, a single U+FEFF BYTE ORDER MARK (BOM) character.

2. Any number of comments and ASCII whitespace.

3. A DOCTYPE.

Environment

Extension	1.1.0
VSC	code-1.100.2-1747260629.el8.x86_64

Footnotes

1. html.spec.whatwg.org/multipage/syntax.html#writing ↩