The study of the relation between syntactic structure and phonological representation has attracted the attention of many phonologists in the past few years. One important contribution to this field of study is Chen's (1987) work on Xiamen Chinese tone sandhi domains. He suggests that the syntax–phonology relation appeals to syntactic information such as category types and the edges of syntactic bracketings. This insight has been further elaborated in the general theory of the syntax—phonology relation of Selkirk (1986). In this theory, the relation between syntactic structure and prosodic structure above the foot and below the intonational phrase is defined in terms of the edges of syntactic constituents of designated types. More precisely, this theory incorporates two hypotheses. One is that there are designated category types in syntactic structure with respect to which one end (Right or Left) of the designated category is relevant in the formulation of a prosodic constituent C, which extends from one instance of the appropriate end (R/L) of the designated category to the next. This hypothesis has been called the End Parameter.