Firefox implements many web standards, including HTML4 (almost full HTML5), XML, XHTML, MathML, SVG 2 (partial),[62][63] CSS (with extensions),[64] ECMAScript (JavaScript), DOM, XSLT, XPath, and APNG (Animated PNG) images with alpha transparency.[65] Firefox also implements standards proposals created by the WHATWG such as client-side storage,[66][67] and the canvas element.[68] These standards are implemented through the Gecko layout engine, and SpiderMonkey JavaScript engine.