brief description of HTML5 (HyperText Markup Language 5)

HTML standard (originally created in 1990 and most recently standardized as HTML4 in 1997)
Its core aims have been to improve the language with support for the latest multimedia (while keeping it easily readable by humans) and consistently understood by web browsers, parsers etc...
HTML5 is intended to subsume not only HTML4, but XHTML1 and DOM2HTML (particularly JavaScript) as well.
HTML5 adds many new syntactical features.

They are designed to enrich the semantic content of documents. New attributes have been introduced for the same purpose, while some elements and attributes have been removed. 

HTML5 spécifie 2 syntaxes d'un modèle abstrait défini en termes de DOM (Document Object Model) : HTML5 et XHTML5.

Le langage comprend également

a) une couche application avec de nombreuses API, 

b) ainsi qu'un algorithme afin de pouvoir traiter les documents à la syntaxe non conforme.