def csp_property(key: str) -> t.Any:
    """Return a new property object for a content security policy header.
    Useful if you want to add support for a csp extension in a
    subclass.
    """
    return property(
        lambda x: x._get_value(key),
        lambda x, v: x._set_value(key, v),
        lambda x: x._del_value(key),
        f"accessor for {key!r}",
    )
Return a new property object for a content security policy header.
    Useful if you want to add support for a csp extension in a
    subclass.
    
src/werkzeug/datastructures/csp.py