def validate_manifests(dist, attr, value):
    """Verifies that ``value`` is an expected mapping of package to
    :class:`sassutils.builder.Manifest`.

    """
    try:
        Manifest.normalize_manifests(value)
    except TypeError:
        raise distutils.errors.DistutilsSetupError(
            attr + "must be a mapping object like: {'package.name': "
            "sassutils.distutils.Manifest('sass/path')}, or as shorten form: "
            "{'package.name': ('sass/path', 'css/path'}), not " +
            repr(value),
        )
Verifies that ``value`` is an expected mapping of package to
    :class:`sassutils.builder.Manifest`.