Where do I look if I want to add my own elements ?

[Gaibhne]

I would like to add more elements other than the default 'heading', 'lines' and 'page break', and I am not averse to learning a bit of programming to get there, and possibly turn it into a PR if that is something that would be appreciated. But as this isn't my ecosystem, it would be helpful if someone more familiar with the project layout could help me get started by pointing out where in the project that kind of thing is currently done/where I would add new/additional things.

[gmg]

I would suggest looking at src/pdf/components/itinerary.jsx

That is where you will find the functions and styles for rendering items and empty lines.