A copy of at most the next n characters of the input still to be tokenized, fewer at its end.
A copy of at most the next n characters of the input still to be tokenized, fewer at its end.
Meant for a custom ErrorHandling instance to look at what failed to match any token rule, e.g. to pick a recovery strategy based on what comes next. Only the requested characters are read and copied, and the result is safe to keep after the callback returns.
