I believe Kevin is referring to the formatting of derivatives of tensors in the Tensorial Application. The following is a mockup of the formatting for tensors and the plain partial derivative of tensors. For tensors:

MakeBoxes[tensor[A_, up_List, down_List], 
  form : StandardForm | TraditionalForm] := 
 Module[{newdown = down, newup = up, makespace}, 
  makespace = If[#1 === Void, Style[#2, ShowContents -> False], #1] &;
   newup = Inner[makespace, newup, newdown, List]; 
  newdown = 
   Inner[makespace, newdown, newup, 
    List]; (InterpretationBox[#1, #2, Editable -> False, 
      BaseStyle -> {AutoMultiplicationSymbol -> False}
      ] &) @@ {SubsuperscriptBox[MakeBoxes[A, form],
     RowBox[(MakeBoxes[#1, form] &) /@ newdown], 
     RowBox[(MakeBoxes[#1, form] &) /@ newup]], Tensor[A, up, down]}]

And for plain partial derivatives:

DifSym = ",";
MakeBoxes[partialD[t_, indices_], 
  form : StandardForm | TraditionalForm] :=
 Module[{windx = Flatten[{indices}]},
  If[MatchQ[t, tensor[_, _, _] | tensor[f_Symbol]],
   InterpretationBox[#1, #2, Editable -> False] & @@ {SubscriptBox[
      MakeBoxes[t, form], 
      RowBox[{DifSym, RowBox@(MakeBoxes[#, form] & /@ windx)}]], 
     partialD[t, indices]},
   InterpretationBox[#1, #2, Editable -> False] & @@ {SubscriptBox[
      RowBox[{"(", MakeBoxes[t, form], ")"}], 
      RowBox[{DifSym, RowBox@(MakeBoxes[#, form] & /@ windx)}]], 
     partialD[t, indices]}]]

The following statements format properly in Mathematica 9.0.1

tensor[A, {Void}, {a}]
partialD[tensor[A, {Void}, {a}], {j, k}]

I have found that the performance of Mathematica 10.1 is impaired enough that I have reverted to Mathematica 9.0.1.