Parameter on graph_info


I’m trying to create some custom graphics for a more general usage. This meas I have services with a different number of metrics but all the metrics follow a convention.
I at lease 1 metrics does not exits, a graph isn’t shown.
In graph_info I played with the parameter omit_zero_metrics, conflicting_metrics, optional_metrics but I had no success to understand how it works.
Is there a description anywhere about these parameter?
regards Robert