Directional Navigation

Hi, folks-

I really like the fact that you address directional navigation (nav-left,
nav-right, nav-up, and nav-down) and quasi-hierarchical navigation. Thanks!

I noticed a related ommission that might be worth considering. In section
15.1.3 Obtaining focus, the SVGDocument interface has focus(), which is
great. It also has next() and previous(), to correspond to nav-index values.
However, there's no directional focus method to match nav-left, nav-right,
nav-up, and nav-down. 

Maybe you could add something like focusDirection(left | right | up | down)
(or the clumsier focusLeft(), focusRight(), focusUp(), focusDown())? I kinda
like the idea of a single parameterized method that could take more than one
argument, so you could do diagonals.

Regards-
-Doug