I can\'t find anything in the HTML5 doc that talks about nested forms. I\'m sure it\'s listed on some page, somewhere (perhaps a changelog
The HTML5 document does mention it in the section you link above:
Content model Flow content, but with no form element descendants.
Content model
Flow content, but with no form element descendants.
"Content model" means "what this element may contain". So no, nested forms are not allowed.