def buildUnder(self, command, tokens, index):
        self.verifyCurrentContext(tokens, index) #currentStore, currentFramer, currentFrame exist

        try:
            under = tokens[index]
            index +=1

            self.verifyName(under, command, tokens, index)

        except IndexError:
            msg = "Error building %s. Not enough tokens." % (command,)
            raise excepting.ParseError(msg, tokens, index)

        if index != len(tokens):
            msg = "Error building %s. Unused tokens." % (command,)
            raise excepting.ParseError(msg, tokens, index)

        unders = self.currentFrame.unders

        if not unders: #empty so just append
            unders.append(under)

        elif under != unders[0]: #not already primary
            while under in unders: #remove under (in case multiple copies shouldnt be)
                unders.remove(under)
            if isinstance(unders[0], framing.Frame): #should not be but if valid don't overwrite
                unders.insert(0, under)
            else: #just name so overwrite
                unders[0] = under

        else: #under == unders[0] already so do nothing
            pass

        console.profuse("     Assigned primary under {0} for frame {1}\n".format(
            under,self.currentFrame.name))

        return True
Makes frame the primary under frame of the current frame
dataset/ETHPy150Open ioflo/ioflo/ioflo/base/building.py/Builder.buildUnder