import re


def is_version_base_valid(dotted_ver_no_dev):
    """
    Checks if the base version is a valid format.  This should be roughly
    semver per the notes in `version.py`.

    Args:
      dotted_ver_no_dev (str): The version string to check, such as `v1.2.3-4`.
        This should exclude anything after the `+` sign if applicable.

    Returns:
      (bool): True if version string is a valid format; False otherwise.
    """
    return re.match(r'^v[0-9x]+.[0-9x]+.[0-9x]+(-[0-9a-z]+)?$',
            dotted_ver_no_dev) is not None