-M is for mouse events.
List of Keys
Collected from this source file
C-<key> Hold Control + Key
M-<key> Hold Meta + Key
F1 F1
F2 F2
F3 F3
F4 F4
F5 F5
F6 F6
F7 F7
F8 F8
F9 F9
F10 F10
F11 F11
F12 F12
IC Insert
DC Delete
Home Home
End End
NPage Next Page / Page Down
PageDown Next Page / Page Down
PgDn Next Page / Page Down
PPage Previous Page / Page Up
PageUp Previous Page / Page Up
PgUp Previous Page / Page Up
BSpace Backspace
BTab Back Tab
Enter Enter
Escape Escape
Space Space
Tab Tab
Up Up
Down Down
Left Left
Right Right
KP* Keypad *
KP+ Keypad +
KP- Keypad -
KP. Keypad .
KP/ Keypad /
KP0 Keypad 0
KP1 Keypad 1
KP2 Keypad 2
KP3 Keypad 3
KP4 Keypad 4
KP5 Keypad 5
KP6 Keypad 6
KP7 Keypad 7
KP8 Keypad 8
KP9 Keypad 9
KPEnter Keypad Enter
MouseDown1 Mouse Down 1
MouseDown2 Mouse Down 2
MouseDown3 Mouse Down 3
MouseUp1 Mouse Up 1
MouseUp2 Mouse Up 2
MouseUp3 Mouse Up 3
MouseDrag1 Mouse Drag 1
MouseDrag2 Mouse Drag 2
MouseDrag3 Mouse Drag 3
MouseDragEnd1 Mouse Drag End 1
MouseDragEnd2 Mouse Drag End 2
MouseDragEnd3 Mouse Drag End 3
WheelUp Mouse Wheel Up
WheelDown Mouse Wheel Down