Just like a program is extensible if its classes are extensible, a written work's extensibility, the ability to expand and to branch out at a later time, is largely dependent upon its pieces. Is a word, or a sentence, or a theme used in more than one piece? Do pieces foreshadow pieces, or allude to pieces that are outside the work? These are central extensibility issues.( i write | i program | i have a homepage | i take an english class )