code: func (g GridType) YRange() (min, max float64) {
  	min = g.yTicks[0]
  	max = g.yTicks[len(g.yTicks)-1]
  	return
  }
docs: // YRange returns the minimum and maximum values for the current tickmark
  // sequence. These correspond to the data values of the graph's bottom and top
  // edges.