It would be fascinating to instrument a programming text editor to capture the entire chain of user input. Then go through that log and determine: 1. How many

It would be fascinating to instrument a programming text editor to capture the entire chain of user input. Then go through that log and determine: 1. How many edits don't preserve the AST structure of a program. Changing a leaf expression to a different expression does, as does, say, changing a `for` loop to a `while` loop. But cutting the `(cond)` part of `if (cond)` out (including the parentheses) and hoisting it to a separate expression does not because now those parentheses mean something different. 2. How often the program is in a grammatically invalid state across multiple edits. I suspect fans of always-valid visual editors massively underestimate the size of both of those.