All of these tests are invalid HTML. They are all compatability issues.
The following three cases should be identical, including the top and bottom spacing from the dividing bars:
FONT in P in DIV
P in FONT in DIV
P in DIV in FONT
The section below is the same, except that the outer DIV in each case has been give a black border, P elements have been given yellow borders, DIV elements aqua borders, FONT elements lime borders, and FONT elements are prefix and suffixed by ">>>" and "<<<":
FONT in P in DIV
P in FONT in DIV
P in DIV in FONT
End.