def _checkRefs(self, refs, errorMsg):
        """Check a list of references found in a sub or pos rule."""
        flatRefs = []
        self._flattenRefs(refs, flatRefs)
        for ref in flatRefs:
            # trailing apostrophes should be ignored
            if ref[-1] == "'":
                ref = ref[:-1]
            if ref not in self.refs:
                print errorMsg % ref
                # insert an empty instruction so that we can't end up with an
                # empty block, which is illegal syntax
                super(FilterFeatureWriter, self).rawText(";")
                return False
        return True
dataset/ETHPy150Open google/roboto/scripts/lib/fontbuild/features.py/FilterFeatureWriter._checkRefs/original