We first prove an extremal propertyof the infiniteFibonacci*word f: the family of the palindromic prefixes{hn | n ≥ 6}of fis not only a circular code but “almost” a comma-free one(see Prop. 12 in Sect. 4).We also extend to a more general situationthe notion of a necklace introducedfor the study of trinucleotides codes on the genetic alphabet,and we present a hierarchyrelating two important classes of codes,the comma-free codes and the circular ones.