The "body-box" is a box to keep the text from getting wider than the tune. Without it the text would go out to the edge of the window. Next comes the first abc section which contains the formatting parameters buut nothing that prints.
Here’s some non-abc text in between the two abc sections. This was part of an effort to develop a better set of chords for this tune than we had available previously.
And that’s the end. We’ve used CSS styles, abc code, and mixed abc and HTML together. You could easily change settings or paste in a different tune if you wanted to experiment with this. Just pay attention to whether there are any extra line breaks due to copying from a PDF.