Description
Breaking off of #1668 ...
Multiple users have requested what amounts to the ability to have multiple legends, within the current concept of "each trace has a single legend item which appears in a single legend". This could be implemented by adding a legend attribute to each trace that would operate similarly to the xaxis attribute, and a corresponding legend2, legend3 series of attributes in the layout. This is distinct from the idea of having a legend for size and one for symbol etc, as in that case each item would refer to multiple traces, and each trace would be represented by multiple items.
The major challenge here is the default positioning of legend2 if present... we could do something really ugly like just having it default to the position of the first legend and forcing users to position them manually, but having it "stick to the bottom" is probably a much more graceful solution, if more complex to implement.