One of the most important, and most confusing, aspects of frames is the parent/child relationships of frames, framesets, and the windows that contain them. The first frameset placed in a window has that window as its parent.
A frameset also can host another frameset, in which case the initial frameset is the parent. Note that a top-level frameset itself is not named, but a frameset’s child frames can be named. Frames can be referred to by name or as an index of the frames array.