Estive a ler o [1] para uma visão das alterações de estrutura, elementos e atributos novos, alterados ou removidos, etc, entre as especificações 4 e 5 do HTML.
Algumas notas:
elementos block level
HTML5 has defined more strict content models for elements such as div and li. These elements can now contain either “block level” or “inline level” content,
but not both.
elementos novos
…the input element’s type attribute can now have the following new values which enable a bunch of new native controls people can use…
atributos novos
A new autofocus attribute can be specified on the input (except when the type attribute is hidden), select, textarea and button elements. It provides a declarative way to focus a form control during page load.
The new form attribute for input, output, select, textarea, button and fieldset elements allows for controls to be associated with more than a single form.
The new required attribute…
You can now disable an entire fieldset by using the disabled attribute on it.
You can now disable an entire fieldset by using the disabled attribute on it.
elementos removidos
applet has been obsoleted in favor of object. center font frame frameset noframes noscript (only dropped in XHTML5) u
DOM
As HTMLDocument e HTMLElement ganharam o getElementsByClassName()
Leituras