Developer Journal: squeek.
Rampsliding Is a Quake Engine Quirk in the Same Way That Bunnyhopping Is
Here’s a snippet:
The obvious assumption would be that [rampsliding] is an intentional feature that uses things like the slope of the surface and the player’s velocity to determine when a player is rampsliding, but that is not the case. In fact, in the same way that bunnyhopping was likely an unintentional quirk of the ‘air acceleration’ code, rampsliding was likely an unintentional quirk of the ‘categorize position’ code.