import re


def _is_pull_request_base_branch_match(pull_request: dict, base_branch: str) -> bool:
    """
    Determine if the pull request represents a notification for a base branch we should consider.

    :param pull_request: Pull request section of payload to examine
    :type: :class:`~dict`
    :param base_branch: Regular expression to match base branches to accept
    :type: :class:`~str`
    :return: Boolean indicating pull request state
    :rtype: :class:`~bool`
    """
    base = pull_request.get('base')
    if not base:
        return False
    ref = base.get('ref')
    return ref and re.match(base_branch, ref) is not None