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MP3 was also covered by a bunch of patents, so you had to license it for a fair bit of money; those patents have finally expired now. Ogg and Vorbis have always been free (and the reference implementation available under an LGPL and later BSD license).

The :required attribute works on radio buttons. If you put required on one radio button (or all), that particular group of radio buttons will be required. On checkboxes, makes each individual checkbox required (to be checked).