There are two tools for this, I would say, each having an advantage depending on whether you are looking at the snippet itself, and wish to apply it elsewhere, or vice versa.
- The Edit ▸ Append Selection to Document command is what will work best for the former. Select the text of the snippet template, and then indicate which item to add the text to. This command keeps you in the original document, so it’s useful if you want to spam this text into a few different places.
- For inserting the contents of another document into the one you’re working on, just drag it from the binder and drop it into the editor, where its text should be inserted. (Note for future reference: in v3 you will need to hold down the Alt key while doing this, otherwise it will insert a link to the document.)