During reviewing I met questions like this one.
Looking at the question alone, it is clear that it is too broad. However, it received a good answer (7-2 votes) that shows that it is answerable (though the answer is a little novel).
So, I incline not to close it (leave open), since it brought a valuable answer for the site.
Question: Is it OK to not consider a question as "too broad" once someone proved that it is answerable by actually providing a good answer?