Actuyally can drag a window with the mouse pointer to the edges of the screen to snap it or maximize it.
Inverse to this feature :the maximized windows can also be dragged down from the title bar to restore them
to their original size.
This behavior exists in Windows 10 and Windows 8 as well even 7.

try on IE normal drag to maximized, Firefox or even on notepad : docking and undocking is possible.

the registry can enable or Disable Drag from Maximized Windows in Windows 7 and Windows 8 and Windows 10

HKEY_CURRENT_USER\Control Panel\Desktop 
DragFromMaximize DWORD
0 = disable
1 = enable

this option is also in control panel (in french go to):
"Panneau de configuration\Options d’ergonomie\Options d’ergonomie\Rendre la souris plus facile à utiliser"

for vfp window i tried on a maximized vfp window:its possible in one direction (normal window docking toward the maximized).
the maximized stays as it and is not draggable by mouse.normal window state can be restored with a dbClick on titlebar (or win+down arrow)
if you create a top level form and drag it by mouse , it can be maximized as docked but the inverse is not possible (exactly as vfp9 window).


windows shortcuts working on vfp9 window (or all windows):
Windows + Up-Arrow: Maximizes the current window.
Windows + Down-Arrow: Restores the original size of a maximized window - for other windows, minimizes them.
Windows + Left-Arrow: Docks the current window on the left side of the screen
Windows + Right-Arrow:Docks the current window on the right side of the screen