def METHOD_NAME(header, charset='iso-8859-1', keep_eols=False,
                  maxlinelen=76, eol=NL):
    """Encode a single header line with Base64 encoding in a given charset.
    Defined in RFC 2045, this Base64 encoding is identical to normal Base64
    encoding, except that each line must be intelligently wrapped (respecting
    the Base64 encoding), and subsequent lines must start with a space.
    charset names the character set to use to encode the header.  It defaults
    to iso-8859-1.
    End-of-line characters (\\r, \\n, \\r\\n) will be automatically converted
    to the canonical email line separator \\r\\n unless the keep_eols
    parameter is True (the default is False).
    Each line of the header will be terminated in the value of eol, which
    defaults to "\\n".  Set this to "\\r\\n" if you are using the result of
    this function directly in email.
    The resulting string will be in the form:
    "=?charset?b?WW/5ciBtYXp66XLrIHf8eiBhIGhhbXBzdGHuciBBIFlv+XIgbWF6euly?=\\n
      =?charset?b?6yB3/HogYSBoYW1wc3Rh7nIgQkMgWW/5ciBtYXp66XLrIHf8eiBhIGhh?="
    with each line wrapped at, at most, maxlinelen characters (defaults to 76
    characters).
    """
    # Return empty headers unchanged
    if not header:
        return header
    if not keep_eols:
        header = fix_eols(header)
    # Base64 encode each line, in encoded chunks no greater than maxlinelen in
    # length, after the RFC chrome is added in.
    base64ed = []
    max_encoded = maxlinelen - len(charset) - MISC_LEN
    max_unencoded = max_encoded * 3 // 4
    for i in range(0, len(header), max_unencoded):
        base64ed.append(b2a_base64(header[i:i+max_unencoded]))
    # Now add the RFC chrome to each encoded chunk
    lines = []
    for line in base64ed:
        # Ignore the last character of each line if it is a newline
        if line.endswith(NL):
            line = line[:-1]
        # Add the chrome
        lines.append('=?%s?b?%s?=' % (charset, line))
    # Glue the lines together and return it.  BAW: should we be able to
    # specify the leading whitespace in the joiner?
    joiner = eol + ' '
    return joiner.join(lines)