Boundaries for moveStart/moveEnd

[murrayju]

I would like to be able to set a boundary node for the moveStart/moveEnd functions. When the cursor is at the start of my (visible) document, and I ask moveStart to move n words to the left, it goes off into the weeds traversing invisible parts of the DOM that I don't care about for hundreds of ms. There should be an option to provide a boundary node, and traversal should stop at that point.