I'm not 100% sure I understand your question, but basically, I am wrong about the above example being two docs (the first one empty, aside from the comment) because the current (v1.1) YAML spec says so, and well, being the spec and all, it trumps my opinion.

The second link from my updated comment (figure 2.7), and most especially it's caption "_two_ documents in a stream" says it better than I could if I were to try to rephrase.

If comments could be their own documents, that caption would say "four documents in a stream, two of which are empty but have comments".

Hope that helps, - d