Find the closest element that has the `magnet` attribute set to `true`. If there was not such an element found, return the root element of the cell view.
function(el) {

        var $el = this.$(el);

        if ($el.length === 0 || $el[0] === this.el) {

            // If the overall cell has set `magnet === false`, then return `undefined` to
            // announce there is no magnet found for this cell.
            // This is especially useful to set on cells that have 'ports'. In this case,
            // only the ports have set `magnet === true` and the overall element has `magnet === false`.
            var attrs = this.model.get('attrs') || {};
            if (attrs['.'] && attrs['.']['magnet'] === false) {
                return undefined;
            }

            return this.el;
        }

        if ($el.attr('magnet')) {

            return $el[0];
        }

        return this.findMagnet($el.parent());
    }