code: def resolve_ref(cls, domain, env, fromdocname, builder, typ, target, node,
                      contnode):
          
          targets = domain.data['targets'].get(cls.ref_type, {})
          try:
              todocname, targetname = targets[target]
          except KeyError:
              env.warn(fromdocname, "Missing BB reference: bb:%s:%s" % (cls.ref_type, target),
                       node.line)
              return None
  
          return make_refnode(builder, fromdocname,
                              todocname, targetname,
                              contnode, target)
docs: Resolve a reference to a directive of this class