Today I saw a description on iterm2's doc about its tmux integration. It says:
To adjust split panes, you have to enable mouse reporting, even if you don't want it otherwise.
What does mouse reporting mean here? The terminal will report where the mouse index is?
It means that mouse clicks will be reported to whatever is reading the terminal as standard input, the position and click will be encoded in an escape code similar to a special function key. Text mode mouse-aware applications (e.g. aptitude) can then use that to perform functions like any "real" graphical use interface (GUI) programs use a mouse.
Such reporting can be overridden by holding the shift key pressed while performing the mouse action, e.g. if you want to simply select some text instead of passing a drag command to the running application.
