https://dart.dev/language/class-modifiers-for-apis#the-sealed-modifer https://dart.dev/language/class-modifiers-for-apis#the-seale... that first paragraph, i b

https://dart.dev/language/class-modifiers-for-apis#the-sealed-modifer https://dart.dev/language/class-modifiers-for-apis#the-seale... that first paragraph, i believe, addresses your question, with excellent example from munificent in sibling comment.