def gen_rel_xsd_path(branch_path, xsd_path):
    """Generate the relative part of the XSD path that follows under `branch_path`.

    Args:
        branch_path: str
            Absolute path to a branch holding all the XSD files for a single formatId.

        xsd_path: str
            Absolute path to an XSD file under the ``branch_path``.

    Returns:
        path: str

        E.g.:
            branc_path = /schema/isotc211/
            xsd_path = /schema/isotc211/gmd/applicationSchema.xsd
            ->
            gmd/applicationSchema.xsd

    """
    assert xsd_path.startswith(branch_path)
    return xsd_path[len(branch_path) :]