> Whether to include trailing slashes in URLs has been an old argument on the internet. Personally, because I consider the parsing-into-segments concept to be central to path parsing, I prefer excluding the trailing slash. And in fact, Yesod's default (and, at least for now, routetype-rs's default) is to treat such a URL as non-canonical and redirect away from it. I felt even more strongly about that when I realized lots of frameworks have special handling for "final segments with filename extensions." For example, /blog/bananas/ is good with a trailing slash, but /images/bananas.png should not have a trailing slash.

So, this is not an argument in which people can really have an opinion: the URLs have fundamentally different semantics and behaviors with respect to relative paths. If you are talking about "the subresource banana under the resource blog" then you must use /blog/bananas, and the trailing slash is incorrect; in such a case, if you were to have a relative link to "apples" it would bring you to /blog/apples. In contrast, if you are wanting some kind of "default" resource--say, the moral equivalent of an "index.html" as is implemented in many web servers (but has nothing to do with the actual information model of the web)--as a subresource of the subresource bananas, then you must use /blog/bananas/; in such a case, if you were to have relative link to apples, it would bring you to /blog/bananas/apples and to link to /blog/apples you'd have to use ../apples.

FWIW, I absolutely agree that "for the narrow question of blog posts, is a blog post a file or a folder?" to be an interesting argument for which one might have a different opinion than someone else for a reasonable reason, but generalizing it to the concept of URL routing itself is wrong: if you believe a blog post is semantically a folder--which is very reasonable, as a blog post might "contain" a number of media attachments"--and the post itself is part of that folder it would simply be wrong to elide the trailing slash, and web frameworks or content management systems that return the representation of a folder from "inside" that folder without a trailing slash deserve a special circle of www hell :/. My hope is that this author is actually just expressing an opinion on the semantics of a blog post, not some general notion about URLs, but it is certainly written as the latter and it seems like the software they work on is general purpose.

As an example, I personally find the usage on GitHub to not just be "incorrect" but "flagrantly ridiculous": it has decided to make no opinion of whether a trailing slash has any semantic meaning or not, and so relative paths essentially make no sense in the context of their website. Is the landing page of my repository "inside" the folder of my repository, or is my repository itself a resource of sorts that happens to also contains subresources? In the former case, the landing page of other repositories in my organization are siblings of my repository's landing page, and the other information about my repository is a subresource of said landing page; while, in the latter case, the landing page of other repositories in my organization is the aunt/uncle of my repository's landing page, and other information about my repository is a sibling of my repository's landing page. Only one of these is supposed to be true!