Alexandria is organized as the inverse of a Kindle book. Instead of having one big document, that you can interact with through linking to parts of the text, it's a bunch of smaller blocks that can be displayed or exported as a big document. And you can't take one section out of a Kindle book and embed it (along with the link to the original author profile data, such as lightning wallet information) within another book. You can only copy-paste the text or create a link. Only Nostr events can be truly embedded because only they are truly atomic.
It's similar to the difference between a hyperlink (reference to a different web page), and literally copying part of the HTML out of a web page and inserting it into a new webpage, but more absolute, since the inserted HTML stays a separate document and you still have the ability to click on that HTML and open up the originally-containing page. Or to say, "Show me all other pages that contain this page-section. Show me all similar page-sections. Show me all citations of this page section. Show me other page-sections by the author of this page..."