4D Write Pro documents are handled using 4D's object type variables. Object type variables allow attributes and values to added to it. With a 4D Write Pro object custom attributes and values can be assigned to the 4D Write Pro object as long as the attribute is not a reserved attribute. This will allow additional details to be added to a WP object stored and even allow WP objects stored in a table field to have additional attributes to be queried upon.
On a form with a Write Pro Area with the object wpObj assigned to it the following code is ran:
WP SET TEXT(wpObj;"Hello World!";wk append)
The document is then properly displayed in the Write Pro area on the form