Any attribute supported as PHP SVGGraph options may be included as frx attributes also. Checkout the PHP SVGGraph library documentation to fully understand the available options, and identify the actual SVG Graph option you should be using (there are plenty of them).
In your case, I think you're looking for SVG Graph legends. In your Forena FRX file, you should be able to specify the desired legends (say
2nd Legend and
3rd Legend) within the SVG tag of your chart with something similar to this example:
For many more details about how to create charts with Forena, refer to the
reports/help.renderers#frxsvggraph in your own site (which is part of what comes with Forena), or refer to the online equivalent of it.
Note: if you only have 1 legend (say
MyLegend), the SVG tag of your chart should be similar to this example (no need for the suffixes like