1. A method for designing extensible stylesheets, the method comprising: receiving a file including a plurality of elements; identifying one of the elements as a reference; determining if any of the elements except for the reference in the file are identical to the reference; inserting one of identifiers to each of some of the elements when the some of the elements are determined to be identical to the reference, wherein each of the identifiers is different from each other, and thus the some of the elements are uniquely differentiated; and wherein, when the file is used to generate another file, the elements are uniquely identified and converted accordingly in the another file.