If `dropdownToggle` can be used in any element we should modify the demo page. It says:

`Simply put it on the <a> tag of the toggler-element, and it will find the nearest dropdown menu...`

That for me is like it is only meant to use in an `a` tag. If so, `ng-disabled` doesn't work here. If you can actually plug the directive in more element where some of them could support `ng-disabled` (like a button), we should modify the demo to say that is not only usable in an anchor.