Por ahora, no todos los navegadores soportan todas las novedades de HTML5.
Antes de usar un nuevo elemento (etiqueta) o atributo, es conveniente consultar algún sitio web
con información sobre el soporte de HTML5 por parte de los navegadores más importantes:
HTML5 differences from HTML4: HTML is the core language of the World Wide Web. The W3C publishes HTML5, which is the fifth major revision of HTML. The WHATWG publishes HTML, which is a rough superset of HTML5. "HTML5 differences from HTML4" describes the differences of these documents from HTML4, and calls out cases where HTML is different from HTML5.
HTML5 Rocks: HTML5 is the ubiquitous platform for the web. Whether you're a mobile web developer, an enterprise with specific business needs, or a serious game dev looking to explore the web as a new platform, HTML5 has something for you!
The HTML5 test: The HTML5 test score is an indication of how well your browser supports the upcoming HTML5 standard and related specifications. Even though the specification isn't finalized yet, all major browser manufacturers are making sure their browser is ready for the future. Find out which parts of HTML5 are already supported by your browser today and compare the results with other browsers.