Draws horizontal/vertical grid lines or sub-grid lines within the chart
subtick
ChartOption for sub-grid lines (dividing the area between grid lines)
Available attributes: subtick has the same attributes as GridLines (displayLine, color, reliefColor, zeroLineColor) except the subtick attribute itself.
<horizontalGridLine>
<color>$BLUE</color>
<subtick>
<displayLine>true</displayLine>
<color>$LIGHTSKYBLUE</color>
</subtick>
</horizontalGridLine>
<verticalGridLine>
<color>$BLUE</color>
</verticalGridLine>
All elements not affected by the grid line option have been grayed out.