It‘s basically copy pasting but it‘s linked. For example you got a math problem and you create a list rem on how to solve it, one of the items though is a process with its own steps, you already have a rem for that and you want to integrate it directly into your current rem you’re working on. What I usually do in this situation is paste a rem reference and use the full page preview but these are a little limited, you for example can‘t access references within it. It‘s kinda similar to portals but in my opinion distinct enough with a different use. Also how well you recalled the embed rem in a flashcard should influence the intervals of the original rem that got embed
The embed Rem would be directly integrated into the flashcard (just imagine a copy paste) and you have the context of the parent rem. A portal on the other hand teleports you to another rem as I understand it. For example if I have a rem called “how to calculate the distance between a point and a straight line”, make a list flashcard out of it and then want to directly integrate a list flashcard rem called “how to calculate the distance between two points” into the other list, an embed rem would be way more fitting than portals because I can test my knowledge of rem in the context of another rem
Ok I found a workaround for the issue of references inside references that works pretty well for me: I simply referenced list items into the other list instead of the whole rem so I don‘t have to hover over the reference inside the reference to access more information