A <fieldset> element located outside a form (but still a part of the form):
The form attribute specifies one or more forms the fieldset belongs to.
|form||Not supported||Not supported||Not supported||Not supported||Not supported|
Note: The form attribute was supported in Opera 12 and earlier versions, but support was removed in version 15.
The form attribute is new in HTML5.
|form_id||Specifies the form element the <fieldset> element belongs to. The value of this attribute must be the id attribute of a <form> element in the same document.|