With the exception of the predicative PP idioms discussed in Section 34.3, sub I, adpositional phrases cannot undergo comparative/superlative formation. It should be noted, however, that formations like voorstefront and achtersteback do occur. They retain their spatial meaning and do have a kind of superlative meaning, but they no longer function as adpositions; the fact that they can occur in prenominal attributive position, as in (104a&b), shows that they behave instead like true adjectives. Observe that these adjectives are in a paradigm with middelstemiddle (104c), which is not derived from a preposition.