Added a note about the Accept header working differently for content …

…negotiation

src/en/guide/theWebLayer/contentNegotiation.gdoc

@@ -106,6 +106,10 @@ For example, if it sees the accept header above ('application/json') it will set
 
 An accept header of '\*/\*' results in a value of @all@ for the @format@ property.
 
+{note}
+If the accept header is used but contains no registered content types, Grails will assume a broken browser is making the request and will set the HTML format - note that this is different from how the other content negotiation modes work as those would activate the "all" format!
+{note}
+
 
 h4. Request format vs. Response format