I would suggest similar to what other people have suggested where you color the background of the cell red and then just display the literal content of the cell

I would suggest similar to what other people have suggested where you color the background of the cell red and then just display the literal content of the cell. I think it would be reasonable to have this configurable via command line arguments though, so if you like the "NA" that could also be a mode. Perhaps it would make sense to have a "pretty" mode and a "literal" mode (which would also turn off the clever processing of numbers)?