To match the visual aesthetics, perhaps sibling <hr> elements, when children of a <select> element, should be presented as one to the end user.

You can use the following data: URL for demonstration purposes (works at least in Chromium and WebKit on macOS): data:text/xml,<select%20xmlns="http://www.w3.org/1999/xhtml"><option>1</option><hr/><hr/><option>2</option></select>.

This might become more common due to whatwg/html#9124.