You can do this with URLs. For instance, I have just the feeds page of my RSS reader bookmarked.
Please let me know if you can't access it.
Worth noting, after starting, I added a few extra features that I found useful, like mixing query parameters.
javascript:location.href='/about'
An easy way to create a bookmarklet from scratch is to create a bookmark from some other page and then modify the URL.This case is relative to a single baseURL. The poster was proposing to have a bookmark relative to the URL you're currently browsing from, so that you could click "/feeds" from any Miniflux instance you're currently visiting.