[KevinH]

Yes, those error messages are not generated by Sigil. They are generated by the Chrome/QtWebengine browser widget used by Qt. They can not guess where the best "fix" is just where they detect that a "fix" (error) has definitely happened in the first place.

Simple missing < and > chars should also be detectable and reported by using Sigil's simple Well Formed check (aka SanityCheck) in the Validation window. So if in doubt you can get a second opinion.

I assume if a user wanted, instead of using the custom preview injected stylesheet for BeckyEbook's solution the user could simply add that css to their own stylesheet while they debug / build their epubs.