URN 5 text spans are a relatively new innovation by Benja Fallenstein: instead of really having a permanent block of text, we virtualize it by always providing the text with the span, and use URN-5 ids.
This has both advantages and disadvantages: on the other hand, some things may be spoofed (unless care is taken), but on the other hand, it makes several operations easier, without having to worry about the text blocks.