PointerEventData pointerID inconsistency

I’m using PointEventData for both mouse and touch inputs, I do a very simple second touch simulation using the right mouse button. I found that pointerID values for touch inputs started on 0, but values for mouse inputs were negative numbers (-1 left, -2 right) instead of the expected 0,1. Is there any purpose on this?

It comes in handy for cross-platform dev. You wouldn’t want the middle mouse button and the third finger in multi-touch gesture to read as the same thing to your input system.

See this post if you want just mouse buttons from your input event system.