def apply_mirroring(storage, debug):
    """Applies L4: mirroring

    See: http://unicode.org/reports/tr9/#L4

    """
    # L4. A character is depicted by a mirrored glyph if and only if (a) the
    # resolved directionality of that character is R, and (b) the
    # Bidi_Mirrored property value of that character is true.
    for _ch in storage['chars']:
        unichar = _ch['ch']
        if mirrored(unichar) and \
                _embedding_direction(_ch['level']) == 'R':
            _ch['ch'] = MIRRORED.get(unichar, unichar)

    if debug:
        debug_storage(storage)