Multi-Level Category Labels on X-Axis

[kurt fichtman]

Is it possible to display a Category and Subcategory label on the X-axis in C3?  I can't find any documentation for it.  Here's an example of the chart I created in excel that I want to create in our software using C3.  In the pic below, you can see that there are multiple Categories (Vendor Products) grouped with scoring across multiple Subcategories on the X-axis. Can anyone help me out?