Xproc uses the word library in a slightly different way to that which I am accustomed. For that reason, and because the (to me) more normal interpretation, a repository of useful information (steps in this case), is so useful, I believe it is worth spending some time looking at how libraries are created and used. James started the ball rolling. Look at how he is starting to create an almost Lisp like creation. Starting with a single step, then building up towards what might become a significant piece of code. First though, the 'standard' way of using libraries, as per Xproc, which if you look at it, is a library of step declarations? This is the official 'library' which defines Xproc at the current version. It is worth reading 2.13 of Xproc a couple of times to see how version changes may affect an authors pipelines.