Framesets may be nested to any level.
In the following example, the outer FRAMESET divides the available space into three equal columns. The inner FRAMESET then divides the second area into two rows of unequal height.
<FRAMESET cols="33%, 33%, 34%"> ...contents of first frame... <FRAMESET rows="40%, 50%"> ...contents of second frame, first row... ...contents of second frame, second row... </FRAMESET> ...contents of third frame... </FRAMESET>