add slicing of tuples of matrices

src/args.jl

@@ -1750,10 +1750,15 @@ function slice_arg!(
     v = get(plotattributes_in, k, plotattributes_out[k])
     plotattributes_out[k] =
         if haskey(plotattributes_in, k) &&
-           typeof(v) <: AMat &&
-           !isempty(v) &&
            !(k in _plot_args)
-            slice_arg(v, idx)
+           if typeof(v) <: AMat &&
+           !isempty(v)
+                slice_arg(v, idx)
+            elseif typeof(v) <: NTuple{2, AMat}
+                (slice_arg(v[1], idx), slice_arg(v[2], idx))
+            else
+                v
+            end
         else
             v
         end

src/utils.jl

@@ -417,7 +417,7 @@ ok(tup::Tuple) = ok(tup...)
 function make_fillrange_side(y::AVec, rib)
     frs = zeros(axes(y))
     for (i, yi) in pairs(y)
-        frs[i] = yi + _cycle(rib, i)
+        frs[i] = yi .+ _cycle(rib, i)
     end
     frs
 end

test/test_pipeline.jl

@@ -32,5 +32,6 @@ end
             @test plot(data4; NamedTuple{tuple(attribute)}(Ref(mat))...)[1][i][attribute] ==
                   [2(i - 1) + 1, 2i]
         end
+        @test plot(data4, ribbon = (mat, mat))[1][i][:ribbon] == ([2(i - 1) + 1, 2i], [2(i - 1) + 1, 2i])
     end
 end