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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def parse_OWS(header: str, pos: int) -> int: """ Parse optional whitespace from ``header`` at the given position. Return the new position. The whitespace itself isn't returned because it isn't significant. """

    # There's always a match, possibly empty, whose content doesn't matter.
    match = _OWS_re.match(header, pos)
    assert match is not None
    return match.end()