This is useful for keeping track of what has happened previously as HTTP protocol doesn't keep any memory of past transactions. Usually the hidden value is placed in the form by a CGI program. Clicking the image submits the form including the coordinates of the mouse pointer. When you turn one radio button on, you turn all the other ones off. Reset Displays a reset button that resets all the fields in the form to their defaul values.
SIZE specifies the number of displayed text lines.
The default is 1, for more than 1 the list is displayed as a scroll box. The option selected is the value sent when the form is submitted. If you put a message within the element, it will be displayed as an initial value. Another type of form of a sort is the isindex element. It isn't used within the FORM element.