HTML5: Differences from HTML 4.01

The following is a cursory list of differences and some specific examples.

• New parsing rules: oriented towards flexible parsing and compatibility; not based on SGML
• Ability to use inline SVG and MathML in text/html
• New elements: article, aside, audio, canvas, command, datalist, details, embed, figcaption, figure, footer, header, hgroup, keygen, mark, meter, nav, output, progress, rp, rt, ruby, section, source, summary, time, video, wbr
• New types of form controls: dates and times, email, url, search, color
• New attributes: ping (on a and area), charset (on meta), async (on script)
• Global attributes (that can be applied for every element): id, tabindex, hidden, data-* (custom data attributes)
• Forms will get support for PUT and DELETE methods too instead of just GET and POST (see Representational State Transfer for use cases)
• Deprecated elements will be dropped altogether: acronym, applet, basefont, big, center, dir, font, frame, frameset, isindex, noframes, s, strike, tt, u