The split screen is really working ?

[quirky_Canvas5DCA]

I have deletet more than half of my code and nothing is changing on split/live. I can see the modification only on saved file...

[Jon Fritz]

Hitting F5 while working in Live View should force it to update.

If that doesn't work, you may need to restore preferences

[Nancy OShea]

When working with PHP files, you must save regularly (Ctrl/Cmd + S) to commit changes to scripts.

If you need to undo changes later, you can with Ctrl/Cmd + Z.  See Preferences > General for more options on Undo and maximum History states.

I'm a stickler for saving regularly as we experience many power disruptions. Better safe than sorry.