Approaches to bound pronominals in HPSG reflect a strict dichotomy between postlexical clitics and lexical (or phrasal) affixes, a distinction already drawn in cliticisation theories developed by Miller (1992) or Halpern (1995). Motivated by the rigorous application of the diagnostic criteria suggested in Zwicky and Pullum (1983) and Miller (1992), clitics in Romance languages are treated as lexical afixes, whose morphological and morphosyntactic properties are derived entirely within the lexicon (Miller and Sag 1997; Monachesi (1996). Weak pronominals in Polish (Kupsc 1999) and second position clitics in Serbo-Croat (Penn 1999), however, enjoy a much higher degree of syntactic transparency, favouring an analysis in terms of linearisation approaches. In this paper, I will suggest that European Portuguese (EP) represents a transitional type, where clitics have already acquired the morphological properties of lexical affixes, yet, ``the rules governing clitic placement seem to relate more to syntax than to prosody or morphology'' (Spencer 1991, p. 365). I will argue that the distinction between constituent structure and order domains, as drawn in linearisation-based variants of HPSG, provides the necessary tools to model the syntax of transparent affixes, relating EP clitics to both their Romance and Slavic counterparts.