Set Shift-Escape (XTSHIFTESCAPE)

The parameter n must be an integer equal to 0 or 1. If n is omitted, n defaults to 0. If n is an invalid value, this sequence does nothing.

When a terminal program requests mouse reporting, some mouse reporting modes also report the modifier keys that are pressed (control, shift, etc.). This would disable the ability for a terminal user to natively select text if they typically select text using left-click and drag, since the left-click event is captured by the running program.

To get around this limitation, many terminal emulators (including xterm) use the shift modifier to disable mouse reporting temporarily, allowing native text selection to work. In this scenario, however, the running terminal program cannot detect shift-clicks because the terminal emulator captures the event.

This sequence (XTSHIFTESCAPE) allows configuring this behavior. If n is 0, the terminal is allowed to override the shift key and not pass it through to the terminal program. If n is 1, the terminal program is requesting that the shift modifier is sent using standard mouse reporting formats.

In either case, the terminal emulator is not forced to respect this request. For example, xterm has a never and always terminal configuration to never allow terminal programs to capture shift or to always allow them, respectively. If either of these configurations are set, XTSHIFTESCAPE has zero effect.

xterm also has false and true terminal configurations. In the false scenario, the terminal emulator will override shift (not allow the terminal program to see it) unless it is explicitly requested via XTSHIFTESCAPE. The true scenario is the exact opposite: pass the shift modifier through to the running terminal program unless the terminal program explicitly states it doesn't need to know about it (n = 0).