code: function isExternalLinkTarget(target) {
      return target === "_blank" ||
          (target === "_parent" && window.parent !== window.self) ||
          (target === "_top" && window.top !== window.self) ||
          (typeof target === "string" && target !== "_self");
  }
docs: Determines whether the target points to a different window, and thus outside of
  the current instance of the application.
  @param {String} target The value of the link's target attribute.
  @returns {Boolean} true when the target is:
  - "_blank",
  - "_parent", and the parent window isn't the current window,
  - "_top", and the top window isn't the current window.
  - a named window or frame (any other value besides "_self").