Japanese Furigana and Ruby Tag Hider

Automatically hide ruby tags (used for Japanese Furigana) on text (small text above sentences), and show them with the mouse.

// ==UserScript==
// @name        Japanese Furigana and Ruby Tag Hider
// @namespace   autoHideRubyKK
// @author      Kai Krause <kaikrause95@gmail.com>
// @description Automatically hide ruby tags (used for Japanese Furigana) on text (small text above sentences), and show them with the mouse.
// @include	    *
// @version     1.3
// @grant       none
// @run-at      document-end
// ==/UserScript==

var newcss = "ruby rt{ visibility:hidden; } ruby:hover rt{ visibility:visible; }";
if ("\v" == "v") {
    document.createStyleSheet().cssText = newcss;
} else {
    var tag = document.createElement("style");
    tag.type = "text/css";
    document.getElementsByTagName("head")[0].appendChild(tag);
    tag[(typeof document.body.style.WebkitAppearance == "string") ? "innerText" : "innerHTML"] = newcss;
}