function isCapital(key) {
        return key === key.toUpperCase() &&
            key !== key.toLowerCase(); // in case key is a symbol or special character
    }
The default `onHintKey` implementation.

@param {HTMLElement} element the element for which the pressed hint is targeted.
@name Hints.dispatchMouseClick
@see Hints.create

@example
mapkey('q', 'click on images', function() {
    Hints.create("div.media_box img", Hints.dispatchMouseClick);
}, {domain: /weibo.com/i});