Oh okay, so even if you speak a dialect that prefers using 'yw' in the middle of a sentence, you'd still begin a question with 'ydy'? Or is it not really an issue?
Yes, exactly. I suppose if someone wants to write "yw" at the start to form a question, they can, but it's incorrect and won't be taught in this course. It it, however, quite common in South Wales to hear utterances such as "Yw e'n dod neu be?" "Is he coming or what?"