For example, given $(( 08 + 1 )) (or similar) instead of reporting
"expecting end of expression" - the generic error for parse failed,
which happened as this was parsed as $(( 0 8 + 1 )) because the 8
could not be a part of an octal constant, and that expr makes no sense -
instead say "unexpected '8' (out of range) in numeric constant: 08"
which makes the cause of the error more obvious.
NFC for valid expressions, just the error message (and the way the
error is detected).
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