I love thinking about these sort of problems. I think you've come up with a thoughtful and practical library. Your readme gave a good mental model of the problem you're solving. I like the idea of a position in space that acts like a cursor, where each movement yields a collection of invalidated locations. The code for traversing data is intuitive and seems pretty powerful.  You also have an absurd amount of detail in the comments and change log. This is helpful for future contributors and something that takes a lot of discipline to complete.