XUL:Trees Cell Selection

One of our clients has requested the following, and we want to develop it on the trunk and get it checked in. We feel it would be a useful addition to the tree widget.

1) The ability to have a cell based selector in a tree, allowing us to navigate by keyboard across a single row to each adjacent column.

2) The ability to attach an event to the tree (or a cell) that would allow us to know which cell is currently selected when a key (such as enter) is pressed, based on its row and column.