1. The document provides definitions and examples for 55 HTML tags, describing their purpose and any differences between HTML 4.01 and HTML 5 specifications. Key tags covered include headings, paragraphs, lists, links, images, forms, tables and more.
2. Many tags have new or removed attributes in HTML 5 to simplify usage or be replaced by CSS styling, like the <font> tag being replaced by CSS. Frames and <center> are also removed in HTML5.
3. New tags in HTML5 include <video>, <audio>, <canvas>, <footer>, <header> and <nav> to define common page sections, as well as <article>, <aside> and <section>