code: function hasEnoughVerticalRoom(parentChartHeight, positionY) {
              return (parentChartHeight - margin.top - margin.bottom - chartHeight) - positionY > 0;
          }
docs: Checks if the mouse is over the bounds of the parent chart
  @param  {Number}  chartWidth Parent's chart
  @param  {Number}  positionX  Mouse position
  @return {Boolean}            If the mouse position allows space for the tooltip