Using 'E' as the extrapolation character in table_model

I have a question that was raised recently from Cary Renzema (refer mantis 3527)

If I use 'E' as the extrapolation character in $table_model() what should the
behaviour be?
'E' means we error, but exactly what sort of error.

Is it a hard error - do we stop simulation right there.

Or do we only raise the error at the end of the time step, and if so what value
should we return from the table_model. Should it be clamped to the closest
endpoint, or should we use linear extrapolation.

I guess we should detail what happens when using 'E' to remove the ambiguity.

Anyone have comments on what should happen here?

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