Any character other than the digits 1-9 may be preceded by a
reverse solidus '\', and unless the combination has an explicitly
defined expansion the character is included without the solidus.
JSON5 adds \', \0 and \v to the set of defined escapes, and an
escaped newline is omitted from a string.
In the test case Perl uses \13 instead of \v in the output
but it is the correct character (13 octal = 11 decimal = '\v').
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