'Invalidate a nested ``<%def>`` within this template.
Caching of nested defs is a blunt tool as there is no
management of scope -- nested defs that use cache tags
need to have names unique of all other nested defs in the
template, else their content will be overwritten by
each other.'

def invalidate_closure(self, name):

    self.invalidate(name, __M_defname=name)
