maclotsen.com Xerdi

About

I am Erik Nijenhuis. Music was my first love. I have played guitar for over twenty years, and spent a while on the choir-conducting preparatory programme at the conservatory — the run-up to that degree rather than the degree itself. Afterwards I retrained in ICT at a university of applied sciences.

Music never left. I often go to the Prinsentuin to improvise classical music on guitar, baritone ukulele or lute — most often the ukulele, because it is light. You can regularly find me playing on a terrace somewhere, if you are lucky. No guarantees. More recently it has turned into work of a kind: I have started doing music publishing, and I now help maintain lyluatex, the package that sets LilyPond scores inside LaTeX. There is also a book about music and the motion of the planets, still unfinished.

Typesetting music turns out to be document engineering with the volume turned up. Music first, then ICT, and then I turned myself into a Document Automation Architect: LuaLaTeX, standards-conformant PDF, and the infrastructure that produces both reproducibly. I run Xerdi, and I am vice-president of the TeX Users Group.

Most of my work is documents that have to be right rather than merely presentable: invoices, regulatory filings, scientific articles. That work has a particular shape. The output has to be archivable in ten years, the process has to be repeatable by someone who is not me, and the claims a file makes about itself have to be true — a PDF that declares an accessibility standard it does not implement is worse than one that stays quiet.

That last point is why this site is built the way it is. The two axes on the skills pages exist because a single number would have been easier and less true.

Source to conformant PDFA LaTeX document and a YAML payload are rendered by lualatex into a PDF. The PDF/A-4f badge lights up because it always holds; the PDF/UA-2 badge stays unlit because it is only declared where tagging is genuinely on. document.tex + payload.yaml lualatex document.pdf PDF/A-4f PDF/UA-2 not claimed always declared UA-2 asserts a structure tree; it is declared only where tagging is genuinely on.

free software

The LaTeX packages are on CTAN and their sources are on GitHub: lua-placeholders for separating document data from document layout, gitinfo-lua for putting real version information into a typeset document, regulatory for compliance-grade PDF, and comment2tex for typesetting a source file together with its own documentation — the annotated file still runs.

affiliations

Where I belong, my own company first. None of this is paid client work, so none of it appears in the figures on the skills pages — a board seat is not an invoice.

Xerdi — Owner, 2021–present
My own company: free software and document engineering for small and medium businesses. Internal work includes XDP, where every LaTeX concern ends up — document automation, book production, scientific writing, legal and compliance work — and the AI Laboratory (ai-lab), an internal research and automation environment.
— Co-founder, 2026–present
A venture I am co-founding, applying document automation and LaTeX engineering to compliance work.

With Germen M. Haijtema and Ben Stegeman.

TeX Users Group (TUG) — Vice-President, 2025–present
The TUG 2026 group photograph, redrawn as pixel art: nineteen attendees standing in a row in front of the conference venue.
The annual group photograph, TUG 2026 in Calgary.
Nederlandstalige TeX Gebruikersgroep (NTG) — Webmaster and secretary's assistant, present
I maintain the website of the Dutch-language TeX user group, and assist its secretary.
Ten members of the Dutch-language TeX user group in a meeting room, drawn as pixel art, all wearing NTG shirts, with a webcam above the screen behind them.
The Dutch-language TeX user group, in NTG shirts.

The commercial work lives at Xerdi. This site is the person behind it.