org.danielnixon.saferdom.impl.html
The form that this button is associated with.
The form that this button is associated with. If the button is a descendant of a form element, then this attribute is the ID of that form element. If the button is not a descendant of a form element, then the attribute can be the ID of any form element in the same document it is related to, or the null value if none matches.
MDN
https://html.spec.whatwg.org/multipage/forms.html#the-button-element