make extra_kwargs a series kw.

src/args.jl

@@ -281,6 +281,7 @@ const _series_defaults = KW(
                                      #     one logical series to be broken up (path and markers, for example)
     :hover              => nothing,  # text to display when hovering over the data points
     :stride             => (1,1),    # array stride for wireframe/surface, the first element is the row stride and the second is the column stride.
+    :extra_kwargs       => KW(),
 )
 
 

src/backends/pgfplots.jl

@@ -161,6 +161,7 @@ end
 function pgf_series(sp::Subplot, series::Series)
     plotattributes = series.plotattributes
     st = plotattributes[:seriestype]
+    extra_kwargs = plotattributes[:extra_kwargs]
     series_collection = PGFPlots.Plot[]
 
     # function args

src/pipeline.jl

@@ -341,7 +341,7 @@ function _expand_subplot_extrema(sp::Subplot, plotattributes::AKW, st::Symbol)
 end
 
 function _add_the_series(plt, sp, plotattributes)
-    plt.attr[:extra_kwargs] = warnOnUnsupported_args(plt.backend, plotattributes)
+    plotattributes[:extra_kwargs] = warnOnUnsupported_args(plt.backend, plotattributes)
     warnOnUnsupported(plt.backend, plotattributes)
     series = Series(plotattributes)
     push!(plt.series_list, series)