Sentence:  Given two adjacent constituents A and B, two cases must be considered:  A can attach as a left <WSD>subconstituent</WSD> of B;  B can attach as a right <WSD>subconstituent</WSD> of A, or as a right <WSD>subconstituent</WSD> of an active <WSD>subconstituent</WSD> of A. 
Meaning of the word marked with <WSD> tags:  A part or component of a syntactic, morphological, or phonetic constituent.