Use @forward for push! and append!. Add tests for both.

src/axiselements.jl

@@ -538,8 +538,7 @@ end
 Plot(is3d::Bool, incremental::Bool, options::Options, data::PlotData,
      trailing::Tuple) = Plot(is3d, incremental, options, data, collect(trailing))
 
-Base.push!(plot::Plot, items...) = (push!(plot.trailing, items...); plot)
-Base.append!(plot::Plot, items) = (append!(plot.trailing, items); plot)
+@forward Plot.trailing Base.push!, Base.append!
 
 """
     Plot([options::Options], data, trailing...)

src/axislike.jl

@@ -21,8 +21,7 @@ Return the corresponding LaTeX environment name.
 """
 function axislike_environment end
 
-Base.push!(axislike::AxisLike, items...) = (push!(axislike.contents, items...); axislike)
-Base.append!(axislike::AxisLike, items) = (append!(axislike.contents, items); axislike)
+@forward AxisLike.contents Base.push!, Base.append!
 
 (T::Type{<:AxisLike})(contents...) = T(Options(), contents...)
 

src/tikzdocument.jl

@@ -22,8 +22,7 @@ struct TikzDocument
     end
 end
 
-Base.push!(td::TikzDocument, items...) = (push!(td.elements, items...); td)
-Base.append!(td::TikzDocument, items) = (append!(td.elements, items); td)
+@forward TikzDocument.elements Base.push!, Base.append!
 
 """
     $SIGNATURES
@@ -191,7 +190,7 @@ function savepdf(filename::String, td::TikzDocument;
         error("ran latex 5 times without converging, log is:\n$log")
     end
     if run_again
-        savepdf(filename, td; latex_engine=latex_engine, buildflags=buildflags, 
+        savepdf(filename, td; latex_engine=latex_engine, buildflags=buildflags,
                 run_count=run_count+1, tmp = tmp)
         return
     end

src/tikzpicture.jl

@@ -17,8 +17,7 @@ end
 
 TikzPicture(elements::TikzElementOrStr...) = TikzPicture(Options(), elements...)
 
-Base.push!(tp::TikzPicture, items::TikzElementOrStr...) = push!(tp.elements, items...)
-Base.append!(tp::TikzPicture, items::TikzElementOrStr) = append!(tp.elements, items)
+@forward TikzPicture.elements Base.push!, Base.append!
 
 function print_tex(io::IO, tp::TikzPicture)
     @unpack options, elements = tp

test/test_elements.jl

@@ -159,3 +159,22 @@ end
     @test repr_tex(Axis(Options(; print_empty = true))) ==
         "\\begin{axis}[]\n\\end{axis}\n"
 end
+
+@testset "push! and append!" begin
+    plot = Plot(Expression("x"))
+    push!(plot, "a")
+    append!(plot, ["b", "c"])
+    @test plot.trailing == ["a", "b", "c"]
+    axis = Axis()
+    push!(axis, plot)
+    append!(axis, ["non", "sense"])
+    @test axis.contents == [plot, "non", "sense"]
+    picture = TikzPicture()
+    push!(picture, axis)
+    append!(picture, ["some", "thing"])
+    @test picture.elements == [axis, "some", "thing"]
+    document = TikzDocument()
+    push!(document, picture)
+    append!(document, ["stuff"])
+    @test document.elements == [picture, "stuff"]
+end