1. Cancel some outdated HTML4 tags
Including purely display effect tags, such as <font> and <center>, they have been completely replaced by CSS .
Other canceled attributes: acronym, applet, basefont, big, center, dir, font, frame, frameset, isindex, noframes, strike,tt
2. Added some New elements
More intelligent form elements: date, email, url, etc.; More reasonable tags: <section>, <video>, <progress>, <nav>, <meter>, <time>, <aside>, <canvas>, etc.
3. File type declaration
There is only one type, <!DOCTYPE html>
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