This behavior is used to create a button to allowe the user add one or more details items in the page, client side. This because the number of detail item the user need is variable and you cannot add a big quantity of items.
To setup the page for this behavior work I suggest to see the flash tutorial "CreateForm". To work this behavior need you create 2 DIV, the second inside the first and the form fields for the details item must be inside the second DIV. This client behavior, when the user click on the button, get the content of the second DIV and insert a copy in the end of the first DIV to replicate the detail form fields. See the demo
This behavior is very simple, apply to a button a client behavior to enable/disable all the details form field.
You need this because if the user don't want insert one of the detail item you put in the page (insert page) the user must disable this details fields. See the demo