gsk:path-builder-rel-line-to (builder x y)

builder -- a gsk:path-builder instance
x -- a number coerced to a single float with the X offset
y -- a number coerced to a single float with the Y offset

Draws a line from the current point to a point offset from it by x, y and makes it the new current point. This is the relative version of gsk:path-builder-line-to function. Since 4.14