Over the past week I've done some of the initial development work on [CaSSius](https://github.com/MartinPaulEve/CaSSius), the portion of the typesetter for the [Open Library of Humanities](https://www.openlibhums.org) that produces PDF output. The idea here is that, as a publisher, you want to produce one document and then create HTML and PDF from that single source. CaSSius provides two ways to achieve this.