Hi Andy,
the relevant things are already said above. I just want to make a minor remark: One can easily write simple "help functions" to make complicated
pieces of code more understandable, e.g.:
Attributes[makeObviousFrame] =
Attributes[makeObviousTree] = {HoldAllComplete};
makeObviousFrame[expr_] := Map[Framed, Inactivate[expr], {0, -2}];
makeObviousTree[expr_] := TreeForm[Inactive[expr]]
Putting these function in front of some "complicated" expression, e.g.:
makeObviousFrame @
Flatten[mkArray1D /@
Partition[
Select[mccRaw, (NumberQ[#[[1]]] ||
StringMatchQ[#[[1]], "INPLANE" ~~ ___]) &], 28], 1]
makeObviousTree @
Flatten[mkArray1D /@
Partition[
Select[mccRaw, (NumberQ[#[[1]]] ||
StringMatchQ[#[[1]], "INPLANE" ~~ ___]) &], 28], 1]
gives:

Maybe this is helpful.
Henrik