'Describes RankExpressions in the search domain, optionally
limited to a single expression.
:type domain_name: string
:param domain_name: A string that represents the name of a
domain. Domain names must be unique across the domains
owned by an account within an AWS region. Domain names
must start with a letter or number and can contain the
following characters: a-z (lowercase), 0-9, and -
(hyphen). Uppercase letters and underscores are not
allowed.
:type rank_names: list
:param rank_names: Limit response to the specified rank names.
:raises: BaseException, InternalException, ResourceNotFoundException'

def describe_rank_expressions(self, domain_name, rank_names=None):

    doc_path = ('describe_rank_expressions_response', 'describe_rank_expressions_result', 'rank_expressions')
    params = {'DomainName': domain_name}
    if rank_names:
        for (i, rank_name) in enumerate(rank_names, 1):
            params[('RankNames.member.%d' % i)] = rank_name
    return self.get_response(doc_path, 'DescribeRankExpressions', params, verb='POST', list_marker='RankExpressions')
