Double-clicking on the border can undo a maximization.

man/icewm.pod

@@ -1187,22 +1187,26 @@ When they start to flash, release the button to merge the frame tabs.
 
 =back
 
-The title frame of a window also listens for mouse clicks.  Left double
-clicking maximizes the window (C<TitleBarMaximizeButton=1>). Press
-Shift to only maximize vertically. Press Alt+Shift for horizontally.
+The title frame of a window also listens for mouse clicks.  A left
+double-click maximizes the window (C<TitleBarMaximizeButton=1>).
+When Shift is also pressed it only maximizes vertically.
+Press Alt+Shift to maximize horizontally.
+
 Middle double-clicking rolls up the window (C<TitleBarRollupButton=2>).
 Also press Shift to maximize horizontally. If B<TitleBarRollupButton>
 is either 4 or 5 then the scroll wheel controls rolling up or down.
-Pressing a mouse button and moving it will move the window.
-C<Alt+Pointer_Button1> lowers the window.
+
+Press a mouse button on the title bar and drag it to move the window.
+A C<Alt+Pointer_Button1> click lowers the window.
 
 When the mouse is on the window frame then a left click raises the
 window.  Dragging with the left button down resizes the window.
 Clicking the right button pops up the context menu.  Dragging with the
 right button moves the window.
 
 Double-clicking on the frame border (or corner) maximizes just that side
-of the window. Another double-click restores that side.
+of the window. Another double-click restores that side. Double-clicking
+on the border can also undo a maximization in that dimension.
 
 Clicking on the desktop activates a menu.  The middle button shows the
 window list (C<DesktopWinListButton=2>).  The right button shows the