code: function isLeftMouseReleased(event) {
      if ('buttons' in event && isNotIEorIsIE10plus) {
        // http://www.w3.org/TR/DOM-Level-3-Events/#events-MouseEvent-buttons
        // Firefox 15+
        // Internet Explorer 10+
        return !(event.buttons | 1);
      }
      if (isChrome15OrOpera15plus || isSafari6plus) {
        // Chrome 14+
        // Opera 15+
        // Safari 6.0+
        return event.which === 0;
      }
    }
docs: Whether the left mouse is not pressed.
  @param event {MouseEvent}
  @return {boolean} True if the left mouse button is not pressed.
  False if unsure or if the left mouse button is pressed.