One approach to research into the syntax of nominals focuses on parallels between nominals and clauses. Within the generative tradition, the structure of the left periphery of the clause has been well documented as a position for e.g. wh-words and topic and focus (see e.g Rizzi 1997), whereas the left periphery of the nominal has received much less attention. One of the more challenging areas of research within the nominal is the analysis of elements that can occur before the indefinite article, e.g. "such (a book)" and "so interesting (a book)". Another recently studied phenomenon, often taken to be linked to this, is indefinite determiner doubling, i.e. nominal expressions which appear to contain two instances of the indefinite article.