When having a (Linux) terminal in raw mode and pressing cursor keys, ANSI sequences for cursor movement (CUB, CUU …) are produced as expected (and without giving the optional parameter for the length of movement.

Now, then I hold SHIFT or CTRL while I press a cursor key, the sequences have two parameters – e.g.

• SHIFT + Cursor left produces CSI 1;2 D
• CTRL + Cursor left produces CSI 1;5 D

Obviously the second parameter refers to the modifier keys, but where can I find any documentation for that behaviour?