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
attribute specified to override this.
This feature allows authors to work around the lack
of support for nested
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
Returns the element's form owner.
Returns null if there isn't one.