Please correct me if I am mistaken, but it seems there's no way to determine when the cursor has changed position on a document.

In JavaScript, listening for this may look like:
context.document.addEventListener('cursorpositionchange', handleChange, ...);

Ideally, this event would be 'debounced' for performance so that holding the down-arrow-key would not toast your CPU. The event should only be fired once the cursor has stopped for, say, 500 miliseconds.

Use Case
It would be nice to be able to always track the cursor position and, if on a paragraph that I care about, select what content is at the cursor.