@egli have a look at how we did it in zedai-to-epub3 for example:
- https://github.com/daisy-consortium/pipeline-scripts/blob/master/zedai-to-epub3/src/main/resources/META-INF/catalog.xml
- https://github.com/daisy-consortium/pipeline-scripts/blob/master/zedai-to-epub3/src/main/resources/xml/xproc/library.xpl