def islockable():
    """
        Return False when the current context can never be locked or locking
        is not support in your setup.

        For example in Zope3, z3c.dav.lockingutils.DAVLockmanager depends
        on a persistent zope.locking.interfaces.ITokenUtility utility being
        present and registered. If this utility can not be locked be then
        we can never use this implementation of IDAVLockmanager.
        """
