The frame manager maintains a list of all of the frames available. This includes the main frames in all of the windows (called '<window_name>_window_frame') and all frames created by loaded content. If you load a frameset, then its frames are added to the frame manager and can be accessed via load_item_in_frame.
All frames are loaded in order. If there are two successive calls to load_item_in_frame in a script, any frames created implicitly be the item loaded in the first call are created first.
Frames can also be connected to particular queries, so that the frame's contents always reflect the current item in that query. (see Database)