Requirements: Need a story for optional and repeated syntax pieces

https://code.world/#PnQkjrztp45GAom-7ardWUA fails to check, despite having two declarations that appear, at first glance, to match the template. At first, I thought this was a failure to consider non-toplevel declarations. But it's quite the opposite! The non-toplevel declaration of `b` matches. It's the declaration of `a` that fails to match! The reason: the template has no where clause, but the definition of `a` does have a where clause. Therefore, it's not a match.

This is surprising to me, but I'm not sure how to specify exactly the behavior that I do want.

Inizia con l’esempio CodeWorld collegato e confronta il modello con le dichiarazioni di `a` e `b`, inclusa la clausola where. Chiarisci il comportamento previsto per gli elementi sintattici opzionali e ripetuti, quindi documenta i requisiti concordati e usa l’esempio per confermare che il comportamento di matching risultante sia corretto.

Scritto dal modello di indicizzazione a partire dal testo della issue.