This half page arrangement:
[Frame1][F2]
[Frm3][Frm4]
[F5][Frame6]

Rearrangable to:
[Frame 1]
[F2|Frm3]
[Frm4|F5]
[Frame 6]
on a full page,
[Frame1][F2][Frm3]
[Frm4][F5][Frame6]
on a quarter page, and
[Frm3][Frm4]
[F5][Frame6]
on a third of a page.

Used by many major comic strips, including, illogically (as it was used to make newspaper space flexible), Sluggy Freelance.

Invented by Bill Watterson
eduar09: I got the impression from the tenth anniversary book that he was at the very least claiming credit for it, later having rejected it.