The document discusses semantic HTML5 and how it differs from traditional HTML. Semantic HTML5 uses newer elements like <header>, <footer>, <nav>, <article>, and <section> that more accurately describe the content they contain. This makes the code more readable for humans and machines. It allows content to be structured into logical document outlines and hierarchies without using generic <div> elements. While browser support for all new elements may not be complete, techniques like HTML5 shiv can help older browsers recognize them. The document also covers some new form input types and attributes introduced in HTML5.