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michael-n-cooper
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Add meter example for issue 1105 (pull #1190) Resolves #1105 by adding a CPU meter display that implements the meter pattern.
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‎examples/meter/css/meter.css

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[role=meter] {
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padding: 2px;
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width: 200px;
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height: 40px;
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border: 2px solid black;
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border-radius: 5px;
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}
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.fill {
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width: 100%;
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height: 100%;
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box-sizing: border-box;
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border: 2px solid black;
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border-radius: 3px;
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background-color: black;
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}

‎examples/meter/js/meter.js

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var Meter = function (element) {
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this.rootEl = element;
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this.fillEl = element.querySelector('.fill');
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// set up min, max, and current value
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var min = element.getAttribute('aria-valuemin');
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var max = element.getAttribute('aria-valuemax');
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var value = element.getAttribute('aria-valuenow');
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this._update(parseFloat(min), parseFloat(max), parseFloat(value));
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};
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/* Private methods */
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// returns a number representing a percentage between 0 - 100
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Meter.prototype._calculatePercentFill = function (min, max, value) {
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if (typeof min !== 'number' || typeof max !== 'number' || typeof value !== 'number') {
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return 0;
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}
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return 100 * (value - min) / (max - min);
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};
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// returns an hsl color string between red and green
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Meter.prototype._getColorValue = function (percent) {
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// red is 0deg, green is 120deg in hsl
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// if percent is 100, hue should be red, and if percent is 0, hue should be green
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var hue = (percent / 100) * (0 - 120) + 120;
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return 'hsl(' + hue + ', 100%, 40%)';
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};
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// no return value; updates the meter element
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Meter.prototype._update = function (min, max, value) {
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// update fill width
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if (min !== this.min || max !== this.max || value !== this.value) {
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var percentFill = this._calculatePercentFill(min, max, value);
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this.fillEl.style.width = percentFill + '%';
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this.fillEl.style.color = this._getColorValue(percentFill);
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}
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// update aria attributes
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if (min !== this.min) {
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this.min = min;
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this.rootEl.setAttribute('aria-valuemin', min + '');
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}
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if (max !== this.max) {
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this.max = max;
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this.rootEl.setAttribute('aria-valuemax', max + '');
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}
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if (value !== this.value) {
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this.value = value;
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this.rootEl.setAttribute('aria-valuenow', value + '');
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}
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};
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/* Public methods */
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// no return value; modifies the meter element based on a new value
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Meter.prototype.setValue = function (value) {
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if (typeof value !== 'number') {
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value = parseFloat(value);
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}
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if (!isNaN(value)) {
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this._update(this.min, this.max, value);
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}
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};
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/* Code for example page */
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window.addEventListener('load', function () {
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// helper function to randomize example meter value
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function getRandomValue (min, max) {
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var range = max - min;
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return Math.floor((Math.random() * range) + min);
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}
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// init meters
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var meterEls = document.querySelectorAll('[role=meter]');
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var meters = [];
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Array.prototype.slice.call(meterEls).forEach(function (meterEl) {
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meters.push(new Meter(meterEl));
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});
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// randomly update meter values
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// returns an id for setInterval
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function playMeters () {
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return window.setInterval(function () {
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meters.forEach(function (meter) {
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meter.setValue(Math.random() * 100);
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});
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}, 5000);
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}
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// start meters
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var updateInterval = playMeters();
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// play/pause meter updates
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var playButton = document.querySelector('.play-meters');
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playButton.addEventListener('click', function () {
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var isPaused = playButton.classList.contains('paused');
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if (isPaused) {
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updateInterval = playMeters();
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playButton.classList.remove('paused');
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playButton.innerHTML = 'Pause Updates';
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}
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else {
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clearInterval(updateInterval);
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playButton.classList.add('paused');
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playButton.innerHTML = 'Start Updates';
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}
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});
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});

‎examples/meter/meter.html

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<title>Meter Example | WAI-ARIA Authoring Practices 1.1</title>
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<!-- Core js and css shared by all examples; do not modify when using this template. -->
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<link rel="stylesheet" href="https://www.w3.org/StyleSheets/TR/2016/base.css">
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<link rel="stylesheet" href="../css/core.css">
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<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.1.0/css/all.css" integrity="sha384-lKuwvrZot6UHsBSfcMvOkWwlCMgc0TaWr+30HWe3a4ltaBwTZhyTEggF5tJv8tbt" crossorigin="anonymous">
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<script src="../js/examples.js" type="text/javascript"></script>
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<script src="../js/highlight.pack.js"></script>
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<script src="../js/app.js"></script>
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<!-- CSS and JS for this example. -->
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<link rel="stylesheet" href="css/meter.css">
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<script src="js/meter.js" type="text/javascript"></script>
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</head>
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<body>
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<nav aria-label="Related Links" class="feedback">
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<ul>
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<li><a href="../../../#browser_and_AT_support">Browser and Assistive Technology Support</a></li>
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<li><a href="https://github.com/w3c/aria-practices/issues/new">Report Issue</a></li>
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<li><a href="https://github.com/w3c/aria-practices/projects/30">Related Issues</a></li>
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<li><a href="../../#meter">Design Pattern</a></li>
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</ul>
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</nav>
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<main>
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<h1> Meter Example</h1>
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<p>The following example of a CPU meter demonstrates the <a href="../../#meter">meter design pattern</a>.</p>
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<section>
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<h2 id="ex_label">Example</h2>
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<div role="separator" id="ex_start_sep" aria-labelledby="ex_start_sep ex_label" aria-label="Start of"></div>
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<div id="example">
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<p>The value of this meter changes every 5 seconds. Use the pause button to stop changes.</p>
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<h3 id="cpu_usage_label">Central Processing Unit (CPU) Usage</h3>
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<p>
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<button type="button" class="play-meters">Pause Updates</button>
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</p>
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<div role="meter" aria-valuenow="90" aria-valuemin="0" aria-valuemax="100" aria-labelledby="cpu_usage_label">
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<svg width="100" height="100" class="fill" aria-hidden="true" version="1.1" xmlns="http://www.w3.org/2000/svg">
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<rect x="0" y="0" width="100%" height="100%" fill="currentColor" />
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</svg>
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</div>
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</div>
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<div role="separator" id="ex_end_sep" aria-labelledby="ex_end_sep ex_label" aria-label="End of"></div>
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</section>
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<section>
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<h2 id="kbd_label">Keyboard Support</h2>
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<p>Not applicable.</p>
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</section>
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<section>
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<h2 id="rps_label">Role, Property, State, and Tabindex Attributes</h2>
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<table aria-labelledby="rps_label" class="data attributes">
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<thead>
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<tr>
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<th scope="col">Role</th>
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<th scope="col">Attribute</th>
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<th scope="col">Element</th>
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<th scope="col">Usage</th>
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</tr>
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</thead>
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<tbody>
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<tr data-test-id="meter-role">
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<th scope="row"><code>meter</code></th>
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<td></td>
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<td>
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<code>div</code>
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</td>
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<td>
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<ul>
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<li>Identifies the element as a <code>meter</code>.</li>
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</ul>
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</td>
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</tr>
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<tr data-test-id="meter-aria-valuemin">
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<td></td>
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<th scope="row"><code>aria-valuemin="NUMBER"</code></th>
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<td><code>div</code></td>
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<td>Specifies the minimum value the meter can have.</td>
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</tr>
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<tr data-test-id="meter-aria-valuemax">
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<td></td>
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<th scope="row"><code>aria-valuemax="NUMBER"</code></th>
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<td><code>div</code></td>
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<td>Specifies the maximum value the meter can have.</td>
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</tr>
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<tr data-test-id="meter-aria-valuenow">
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<td></td>
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<th scope="row"><code>aria-valuenow="NUMBER"</code></th>
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<td><code>div</code></td>
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<td>Specifies the current value of the meter.</td>
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</tr>
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<tr data-test-id="meter-aria-labelledby">
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<td></td>
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<th scope="row"><code>aria-labelledby</code></th>
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<td><code>div</code></td>
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<td>Identifies the element that provides the accessible name of the <code>meter</code>.</td>
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</tr>
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</tbody>
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</table>
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</section>
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<section>
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<h2>Javascript and CSS Source Code</h2>
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<ul>
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<li>
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CSS:
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<a href="css/meter.css" type="text/css">meter.css</a>
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</li>
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<li>
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Javascript:
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<a href="js/meter.js" type="text/javascript">meter.js</a>
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</li>
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</ul>
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</section>
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<section>
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<h2 id="sc1_label">HTML Source Code</h2>
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<div role="separator" id="sc1_start_sep" aria-labelledby="sc1_start_sep sc1_label" aria-label="Start of"></div>
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<pre><code id="source1"></code></pre>
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<div role="separator" id="sc1_end_sep" aria-labelledby="sc1_end_sep sc1_label" aria-label="End of"></div>
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<script>
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sourceCode.add('source1', 'example');
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sourceCode.make();
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</script>
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</section>
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</main>
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<nav>
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<a href="../../#meter">Meter Design Pattern in WAI-ARIA Authoring Practices 1.1</a>
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</nav>
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</body>
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</html>

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