As far as I could find, the spec does not define what the expected behavior should be when neither an accept header nor a $format query parameter is specified in a request. Does the server return the response in a spec defined default format or does the server get to choose which format to return results in.

We should also cover the case of ambiguous Accept headers containing /: currently the Olingo server library responds to requests from IE and Chrome with Atom-XML:

• Internet Explorer sends Accept: text/html, application/xhtml+xml, /
• Chrome sends Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,/;q=0.8
  As application/json isn't explicitly mentioned, they use application/xml