It helps in reducing the set matched of elements in a form of the index. It is a zero based indexing. By zero-based indexing we mean that the indexing begins from zero. First, an element is indexed as zero and thus simultaneously indexing goes on. So we can reduce the set of matched elements on the basis of the index and apply a specific attribute to the particular index. Thus it is a very powerful tool to apply the attribute to a particular element from a group of similar elements.