The form demonstrates the multiple feature. This feature is useful when the user
can enter a variable number of inputs. For instance, in your registration form you can ask for an indeterminate number
of email addresses.
This demo uses the winxp theme.
When you designate an input as multiple, the form adds a '+' button next to it.
When the user clicks the button, the input field is duplicated and the user can enter another field of data.
Next to each of the duplicates is a '-' button. The user can remove that input
field, by clicking the '-' button.
In the form, the name of the added input field is the original name with "-n" appended,
where n indicates the order in which the field was duplicated.
You can use either spformMultiple or spformMultipleInside as the class name. spformMultiple adds the '+' after the
HTML element, spformMultipleInside adds it inside of the element, and in the case of a table, inside a new cell.
To control the proliferation of cloned elements use the spformMultipleLimit property.