&what: Discover Unicode & HTML Character Entities : amp-what is a quick, interactive reference of 14,500 HTML character entities* and common Unicode characters, 8859-1 characters, quotation marks, punct...
Email Standards Project : The Email Standards Project is about working with email client developers and the design community to improve web standards support and accessibility ...
AlsacréationS : Alsacréations est une communauté dédiée à l'apprentissage des standards web (W3C, HTML, XHTML, CSS) ainsi qu'à l'accessibilité numérique
DOM Monster Bookmarklet : DOM Monster is a cross-platform, cross-browser bookmarklet that will analyze the DOM & other features of the page you're on, and give you its bill of ...
This site provides a collection of schemas that webmasters can use to markup HTML pages in ways recognized by major search providers, and that can also be used for structured data interoperability (e.g. in JSON).