The unsafe_html lint rule was not meant for external usage. It was implemented for internal usage, before there was a set of internal lint rules.

This rule is not maintained, and does not have any external design. It is also meant to be used with cannot-ignore and in a VCS where specific owners have rights to specific files. None of this applies to this repo. Additionally, the rule only helps with dart:html elements, which is a library that is not imported anywhere in the flutter/flutter repository.

See also dart-lang/sdk#57099