@EvanHahn Depends on the level of the challenge you are interested in, but some starting points:
* A breakdown of some of the points of ambiguity: https://overengineer.dev/blog/2018/02/01/activitypub-one-protocol-to-rule-them-all.html
* Followup thoughts: https://overengineer.dev/blog/2019/01/13/activitypub-final-thoughts-one-year-later.html
* This thread goes into a lot of the tradeoffs around the linked-data approach: https://socialhub.activitypub.rocks/t/linked-data-undersold-overpromised/2268
* Jennifer++ drew out the process of building a federated app and all of the levels that interact, leading to more spaces for it to go wrong: https://hachyderm.io/@jenniferplusplus/111342566946755633