Filter style keywords according to backend

[jlstevens]

I think this functionality is best expressed with a screenshot:

Note that linewidth applies to matplotlib and line_width applies to Bokeh.

[jlstevens]

In the last commit, I skip filtering if style_opts is an empty list.

The assumption is that things like OverlayPlot don't support styles (although they may support plot options). Applying filtering on OverlayPlot was part of why the tests failed.

Is this assumption reasonable?

[philippjfr]

In the last commit, I skip filtering if style_opts is an empty list.

Sounds reasonable, yes. Not sure why not doing that would make it fail though.

[jlstevens]

Without it, I saw odd things in the Elements notebook...for instance the first overlay with errorbars ended up having red errorbars instead of the usual black ones.

[jlstevens]

Thanks for the last fix! Ready to merge once the tests pass.

[philippjfr]

Okay, tests passing at last. Merging.

[jbednar]

In the future, in cases where multiple backends use the same keyword to mean different things, should we support adding an identifier to specify the backend? E.g. 'bokeh:linewidth=5" or "mpl:linewidth=10"? This could also be used if we wanted to customize the two plots separately, e.g. to choose one color that looks good against mpl's default gray background, and a different color for Bokeh...

[jlstevens]

E.g. 'bokeh:linewidth=5" or "mpl:linewidth=10"?

Seems like a good suggestion - please file an issue for this as a feature request.

[philippjfr]

That does sounds like a good suggestion, although I'd go for something like mpl:(linewidth=5 facecolor='red') bokeh:(line_width=5 fill_color='red') to separate them more cleanly.