This was sufficiently misleading that event our own wxGrid unit tests
used this function in an attempt to start editing a grid cell -- even
though it actually doesn't do it at all.
Unfortunately documenting the surprising semantics of this functions
looks like the best thing we can do because it appears to have always
behaved like this and changing it now to actually show the cell editor
control, i.e. starting to edit the cell, is almost certain to break some
existing code.
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