def find_header(blockquote):
    """Find attributes in a blockquote if they are defined on a
    header that is the first thing in the block quote.

    Returns the attributes, a list [id, classes, kvs]
    where id = str, classes = list, kvs = list of key, value pairs
    """
    if blockquote[0]['t'] == 'Header':
        level, attr, inline = blockquote[0]['c']
        return level, attr, inline