Question about ``concert'' format in Appendix E of TeXbook

On p.412 of TeXbook there is this text:

The author has extended these macros to a more elaborate format that includes special features for listing the members of the orchestra and for program notes,
etc.; in this way it becomes fairly easy to typeset little booklets for concert patrons.
Such extensions need not be discussed further in this appendix, because they don’t
illustrate any essentially new ideas.

The fact that this format is even mentioned in TeXbook means that it can be useful. So, where to find it?