The containing form element, if this element is in a form.
The containing form element, if this element is in a form. If this element is not contained in a form element: HTML5 this can be the id attribute of any <form> element in the same document. Even if the attribute is set on <input>, this property will be null, if it isn't the id of a <form> element. HTML 4 this must be null.
MDN
Identifies a list of pre-defined options to suggest to the user.
Identifies a list of pre-defined options to suggest to the user. The value must be the id of a <datalist> element in the same document. The browser displays only options that are valid values for this input element. This attribute is ignored when the type attribute's value is hidden, checkbox, radio, file, or a button type.
MDN
https://html.spec.whatwg.org/multipage/forms.html#the-input-element