I hate most implementations of those more than fixed bars, I regularly scroll slightly too far when I take a second longer to read a line than I was expecting a

I hate most implementations of those more than fixed bars, I regularly scroll slightly too far when I take a second longer to read a line than I was expecting and need to scroll back to see what I missed; then out of nowhere a massive header pops down and covers both what I was trying to read and the next 3 lines so I have to scroll back even further and any flow state is completely interrupted. Safari on iPhone is one of the few implementations that actually works well, playing round with it a bit now it looks like it has quite a few heuristics to determine when to expand again. I guess most people don't care enough to actually spend the time adding more than just "show on drag down".