An HTML user agent begins processing a form by presenting the document with the fields in their initial state. The user is allowed to modify the fields, constrained by the field type etc. When the user indicates that the form should be submitted (using a submit button or image input), the form data set is processed according to its method, action URI and enctype. When there is only one single-line text input field in a form, the user agent should accept Enter in that field as a request to submit the form.