- In section 2.2, Formal Syntax, the ABNF section includes mention of Postel's
  Law. I know what Postel's Law is, but the reader might not, and there's no
  other reference to it in the document. Perhaps at least an Informative 
  Reference could be added?

- In Section 2.2.1, we have the sentence "If there is more than one group 
  matching the user-agent, the matching groups' rules MUST be combined into 
  one group." What if the combined rules conflict with each other due to a
  misconfiguration by the owner of the robots.txt file?