code: func (g GridType) Pos(xRel, yRel float64) (x, y float64) {
  	x = g.w*xRel + g.x
  	y = g.h*(1-yRel) + g.y
  	return
  }
docs: // Pos returns the point, in page units, indicated by the relative positions
  // xRel and yRel. These are values between 0 and 1. xRel specifies the relative
  // position between the grid's left and right edges. yRel specifies the
  // relative position between the grid's bottom and top edges.