A form-associated element can have a relationship
with a form
element, which is called the element's
form owner. If a form-associated element is
not associated with a form
element, its form
owner is said to be null.
A form-associated element is, by default, associated
with its ancestor
form
element, but may have a form
attribute specified to
override this.
This feature allows authors to work around the lack
of support for nested form
elements.
If a form-associated element has a form
attribute specified, then that
attribute's value must be the ID of a form
element in
the element's owner Document
.
form
Returns the element's form owner.
Returns null if there isn't one.