After reading the documentation on the subject, I still cannot get CellContext->CellGroup to work.
Here's a simple example. (Unfortunately, I cannot easily show cell grouping, so I'll just have to describe the steps verbally as clearly as possible.)
First I evaluate this (which succeeds):
SetOptions[EvaluationNotebook[], CellContext -> CellGroup];
Then, I create two empty input cells, and group them (right-click->Group Cells).
Next, I type (but do not yet evaluate) the following two expressions into these two (now grouped) cells (one expression per cell):
foo = {}; (* first grouped cell *)
AppendTo[foo, 1]; (* second grouped cell *)
Presumably these two cells now share the same context. This will turn out to be wrong.
(FWIW, note that these cells produce no output.)
Lastly, I select the group and evaluate its contents (with shift-enter). The evaluation of the second cell fails with the following error:
AppendTo::rvalue: foo is not a variable with a value, so its value cannot be changed. >>
What am I doing wrong? Is this a bug or a feature?
Here's another, even simpler example. I proceed as before, except that this time both cells in the group contain the same expression:
$Context
(NB: no trailing semicolon!)
Now, when I evaluate the group, the output shows that the two grouped cells have different contexts:
(* Cell$$17872` *)
(* Cell$$17874` *)
One possible clue to what may be going on is the fact that when I evaluate the last pair of grouped cells, the bracket grouping the two cells disappears. What's left are 4 ungrouped brackets, two for the original input cells, alternating with their respective output cells. If I delete the output cells, the grouping bracket reappears. This may be a red herring, since, after all, in my previous example there was no output, and yet the two grouped cells behaved as if their contexts were different.
