From: Mihail on
I write Mathematica programs. Reading of a code with many nests or a
deep code is a difficult problem. I want to suggest a feasible
solution. When I move the cursor through the code then the nearest
part of the code will be highlighted. There is the nearest part of the
code in the nearest level.

Something like this:

Cell[BoxData[
RowBox[{
RowBox[{
RowBox[{"Sin", "[",
RowBox[{
StyleBox["Cos",
Background->RGBColor[0.866667, 0.937255, 1]],
StyleBox["[",
Background->RGBColor[0.866667, 0.937255, 1]],
RowBox[{"2", " ",
RowBox[{"ArcCsc", "[",
RowBox[{"#", "+", "1"}], "]"}],
StyleBox[
RowBox[{
RowBox[{"-", "Pi"}], "/", "2"}],
Background->RGBColor[0.866667, 0.937255, 1]]}],
StyleBox["]",
Background->RGBColor[0.866667, 0.937255, 1]]}], "]"}], "&"}], "/
@",
RowBox[{"{",
RowBox[{"x", ",",
RowBox[{"x", "^", "2"}], ",",
RowBox[{"x", "^", "3"}]}], "}"}]}]], "Input",
CellChangeTimes->{{3.4887160374923267`*^9, 3.4887160772304373`*^9}}]

Sorry, my English isn't good.