enum PointerButton

Modifier bitfield (GLFW mods). Which mouse button an event came from.

The order the compositor forwards them in, which is evdev's BTN_LEFT, BTN_RIGHT, BTN_MIDDLE shifted to zero — and the same numbering GLFW uses, which is what the windowed path was written against. Middle is 2, not 1, and that is the one worth having a name for.