Exporting notebooks inserts unwanted $CellContext. Workaround?

Question

Let's import a notebook:

nb = ImportString["Notebook[{},TrackCellChangeTimes->False]", "NB"]
(* Notebook[{}, TrackCellChangeTimes -> False] *)

All is well so far. Now let's re-export it:

ExportString[nb, "NB"]

Now the output contains

$CellContext`TrackCellChangeTimes -> False

instead of

TrackCellChangeTimes -> False

This happens with every valid notebook or cell option that doesn't already have a corresponding symbol in the System` context, and thus Import creates it in Global` instead.

Why does this happen? What's a reasonable workaround?

Notes:

• I need the notebooks exported with full cache information, so I cannot export them as a plain expression.

• NotebookSave suffers from the same problem.

• The problem goes away if I use "TrackCellChangeTimes" (a string) instead of TrackCellChangeTimes.

  However, cycling such a notebook expression through NotebookPut and NotebookGet "removes" the quotes and converts the string to a symbol again. Thus I do not know how to get strings for such options when importing a notebook.

• I am using Import/Export to post-process notebooks created by the documentation tools and fix things. The unwanted $CellContext causes subtle breakage that I did not even notice until now.

Answer 1

TL;DR;

You can redirect unknown symbols to System` which will be stripped later:

Block[{$Context = "System`"},
 nb = ImportString["Notebook[{},TrackCellChangeTimes->False]", "NB"]
]

---

Digging in boxes' (cell expressions)* typesetting

*in opposite to expressions typesetting e.g.: Global`symbol -> RowBox[{"symbol"}]

That is acutally quite important part of typsetting. So when will the context be stripped? When will $CellContext` appear? Here is a small test:

sample = {
 {#, #, #2, "System`"},
 {#, #2, #2, "System`"},
 {#, "System`", #2},
 {#, #2, #2},
 {#, #2, #2, "System`", #}
 } & @@@ {{"JLink`", "Global`"}, {"Global`", "JLink`"}, 
    {"System`", "JLink`"}, {"FrontEnd`", "Global`"}
 } //  Flatten[#, 1] &;

 result = Block[{$Context = #2, $ContextPath = {##3}}, Reap[
       Module[{str},
        str = 
         ExportString[
          Notebook[{}, Symbol[# <> "TrackCellChangeTimes"] -> False], 
          "NB"];
        str = StringToStream[str];
        Sow[{#, #2, {##3}, Find[str, "TrackCellChangeTimes"]}];
        Close[str];
        ]][[-1, 1, 1]]
     ] & @@@   sample;

result // SortBy[Last] //  TableForm[#, TableAlignments -> Right, 
   TableHeadings -> {None, Style[#, Bold, 15] & /@ {"symbol's context", "$Context",  "$ContextPath", "exported string"}}] &

So the rules seem to be as follows:

Which[

• Symbol's context is System`?

  Leave only the symbol name.

• Symbol's context is the same as current $Context?

  Use $CellContext`symbolName

• Is symbol's context Global`,FrontEnd` or any FrontEnd related?

  Leave only the symbol name.

• True

  Use symbol's full name.

]