RFE: cursors snap to high d/dt edges

[jwise]

It would be very nice for cursors to 'snap' to high d/dt edges when being dragged around. One strawman proposal:

• When the mouse pointer is near (in both X and Y) to a high d/dt edge (maybe high d/dt including a low pass filter for current horizontal scale?) that is "large enough" (some percentage of the current vertical display scale?), then the cursor repeatably snaps to the center of that edge.
• Holding down a modifier key (shift?) can temporarily override the snapping behavior. (Does this need to change for keyboardless applications? Perhaps a toolbar button, or a checkbox in the 'cursors' menu in the rightclick menu?)