See Mouse for details.
Note: This mode will make the terminal unresponsive if not used correctly.
🛈 Mouse actions with shift held are used for text selection. By default mouse actions with exactly ctrl held are used for xterms internal menu. Alt and ctrl-alt are passed to the application. 🛈 Alt + middle click is bound to a hard reset of the terminal in the default configuration. 🛈 Mouse wheel left and right are reported as codes 68 and 69 since version 338. 🛈 Additional mouse buttons are reported since version 342. Correct button up reporting for additional mouse buttons since 345.
vte aliases this to mouse down+up tracking ignoring this mode's special behavior.