使用dc.js（d3.js）并尝试将x轴突出显示为0

I want to highlight the xaxis at the value 0 so it's easy to see when values are going negative. I'm trying to do this in a renderlet. I can see tell that the x axis is at 0 when the y1 attribute value is equal to the y2 attribute values. So in the renderlet I'm trying to select the lines, get the y1, y2 values and then when they are equal apply something to the line to make it stand out. Has anyone does this? Is there any easier way. I've got pictures of the element and my selector. I just can't get the y1, y2 attributes from the selector in the renderlet.I want to highlight the xaxis at the value 0 so