HTML5 is not a single feature

Before providing the developer with new features, HTML5 tries to solve core problems that were exposed in previous versions of HTML, namely the programming architecture. Since HTML was not originally created with web application development in mind, as programmers started using it for such purposes, they soon found themselves with very messy code. The application data was heavily mixed with the presentation code, which was in turn tightly coupled with the application logic.

To solve this problem, developers were given Cascading Style Sheets (CSS), which allowed them to separate HTML markup (the information) from how the information was rendered. Thus, the term HTML5 really refers to three separate technologies, namely HTML5 (the new semantic elements or tags), CSS3, and JavaScript (all the new APIs, such as web storage, web workers, and web sockets, to name a few).