In the Tutorial under the Scrivenings section, it says “You cannot make textual edits across document boundaries.” in a yellow Tip box. What does this mean?
Scrivenings mode shows several documents at once. But you can’t, for instance, select and delete a chunk of text that includes pieces of two adjacent documents.
Note that you can merge the documents together and then split them at a different point so that the chunk of text you wanted to delete is all inside one document.