function Highlighter(win, onSelect) {
	    _classCallCheck(this, Highlighter);

	    this._win = win;
	    this._onSelect = onSelect;
	    this._overlay = null;
	    this._multiOverlay = null;
	    this._subs = [];
	  }
Manages the highlighting of items on an html page, as well as
hover-to-inspect.