swfmovie->add() adds instance to the current movie. instance is any type of data : Shapes, text, fonts, etc. must all be add'ed to the movie to make this work.
For displayable types (shape, text, button, sprite), this returns an SWFDisplayItem(), a handle to the object in a display list. Thus, you can add the same shape to a movie multiple times and get separate handles back for each separate instance.
See also all other objects (adding this later), and swfmovie->remove()
See examples in : swfdisplayitem->rotateto() and swfshape->addfill().