The focus of this paper is on ENP-expressions that can be used for annotating ENP scores with user definable information. ENP is a music notation program written in Lisp and CLOS with a special focus on compositional and music analytical applications. We present number of built-in expressions suitable for visualizing, for example, music analytical information as a part of music notation. A Lisp and CLOS based system for creating user-definable annotation information is also presented along with some sample algorithms. Finally, our system for automatically analyzing and annotating an ENP score is illustrated through several examples including some dealing with music information retrieval.