The spec, purposefully, stops short of telling implementations (browsers) how to handle UI. In this article we're looking specifically at
<input type="number"/>, and you might be surprised to learn that the spec specifically says:
This specification does not define what user interface user agents are to use.
It goes on to explain that different languages, cultures, and regions might have good reason to handle numeric inputs differently. So browsers are on their own here, and perhaps this time …