turns, you might mark the one way it \e{can't} go with a cross.)
Alternatively, use the cursor keys to move the cursor. Use the Enter
-key to begin and end keyboard `drag' operations. Use the Space key to
-cancel the drag. Or, hold Control while dragging with the cursor keys
-to toggle segments as you move between squares.
+key to begin and end keyboard `drag' operations. Use the Space,
+Escape or Backspace keys to cancel the drag. Or, hold Control while
+dragging with the cursor keys to toggle segments as you move between
+squares.
Pressing Control-Shift-arrowkey or Shift-arrowkey simulates a left or
right click, respectively, on the edge in the direction of the key.