Title (or label) for legend.

[frankvgompel]

Usually you would want to use the legend to define subsets from a specific category, say a column in a dataframe.

Examples from Plotly:

I suppose the most straightforward approach is a title() method for the legend.

[bircni]

@frankvgompel Could you have a look at my PR and see if this suits you?

[frankvgompel]

Thanks Nicolas, looks quite adequate.