When I incorrectly change card templates in an add-on and try to save them, I can get an error message like this:
anki.errors.CardTypeError: Card template <U+2068>1<U+2069> in notetype '<U+2068>2. Mnemonics<U+2069>' has a problem.<br>See the preview for more information.
The error message is misleading, because it assumes it happens in the context of a note type editor where a preview is present, which is incorrect.
I suggest that Anki returns a more informed message when not in GUI, e.g., “Anki could not parse card template 1 in notetype ‘2. Mnemonics’ correctly. DETAILS.”