I was adding this to my Robots.txt Generator
and went directly to the source
to find out the proper usage:
This directive is independent of the user-agent line, so it doesn't matter where you place it in your file. If you have a Sitemap index file, you can include the location of just that file. You don't need to list each individual Sitemap listed in the index file.
So apparently it just needs to be a single line. It looks like Google et al
would likely support/ignore the use of the user-agent and allow/disallow simply as a matter of creating a more robust handling of various types of robots.txt setups, even if they are improper.
It apparently doesn't matter where in the file it's placed, either. I put it at the end because I think it's the least likely to cause an issue with a badly programmed spider if it's at the end. If it chokes at the beginning, there could be an issue with the rest of the file being ignored. I really doubt it would be a problem, but better safe than sorry.