How does Satteri compare to a standard library like marked (https://github.com/markedjs/marked)?

It depends in what regards you mean, I have some benchmarks here if you'd like to take a look at those: https://github.com/Princesseuh/web-markdown-benchmark

The TL;DR is that `marked` is very light, but a bit on the slower side compared to Sätteri and `markdown-it` (and its forks). I'm not sure how friendly the extensibility is, but Sätteri re-use the same AST format as the unified ecosystem, which might feel more friendly.

Both good options, though!