@classmethod
def declare_core(cls, core):
    """ Add new core in the declared cores

        ::

            RegistryManager.declare_core('Core name')

            -----------------------------------------

            @Declarations.register(Declarations.Core)
            class ``Core name``:
                ...

        .. warning::

            The core must be declared in the application, not in the bloks
            The declaration must be done before the loading of the bloks

        :param core: core name
        """
    if core not in cls.declared_cores:
        cls.declared_cores.append(core)
