Enable spellcheck: Enforces the `spellcheck` attribute to true.

Enable spellcheck 1.01.js

// ==UserScript==
// @name Enable spellcheck
// @version 1.01
// @description Enforces the `spellcheck` attribute to true.
// @namespace https://gist.github.com/3154440/
// @copyright 2012
// @author XP1
// @homepage https://github.com/XP1/
// @license Apache License, Version 2.0; http://www.apache.org/licenses/LICENSE-2.0
// @include http*://*
// ==/UserScript==

/*
 * Copyright 2012 XP1
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*jslint browser: true, vars: true, maxerr: 50, indent: 4 */
(function (window) {
    "use strict";

    function setSpellcheckAttribute() {
        var document = window.document;
        var elements = document.querySelectorAll("html:not([spellcheck=\"true\"]), input[type=\"text\"]:not([spellcheck=\"true\"]), [spellcheck=\"false\"]");

        var i = null;
        var length = elements.length;
        for (i = 0; i < length; i += 1) {
            elements[i].setAttribute("spellcheck", "true");
        }
    }

    window.addEventListener("DOMContentLoaded", setSpellcheckAttribute, false);
}(this));

I posted this script in this thread:

Activating automatic spell checking on input fields in Opera:
http://superuser.com/questions/424075/activating-automatic-spell-checking-on-input-fields-in-opera/