I don't think it would matter, text affinity happens at texts "run" boundaries... so only where formatting changes. Doesn't matter how many attributes each run

I don't think it would matter, text affinity happens at texts "run" boundaries... so only where formatting changes. Doesn't matter how many attributes each run has. I think that is proper way to design the feature, but it does means it's maybe less flexible then you are thinking. You can pick left or right run... you can pick individual attributes within a run with text affinity.