gsk:path-builder-rel-cubic-to (builder x1 y1 x2 y2 x3 y3)

builder -- a gsk:path-builder instance
x1 -- a number coerced to a single float with the X coordinate of the first control point
y1 -- a number coerced to a single float with the Y coordinate of the first control point
x2 -- a number coerced to a single float with the X coordinate of the second control point
y2 -- a number coerced to a single float with the Y coordinate of the second control point
x3 -- a number coerced to a single float with the X coordinate of the end of the curve
y3 -- a number coerced to a single float with the Y coordinate of the end of the curve

Adds a cubic Bézier curve from the current point to x3, y3 with x1, y1 and x2, y2 as the control points. All coordinates are given relative to the current point. This is the relative version of the gsk:path-builder-cubic-to function.