anchor.diff:      use response = response
       let stream = response.GetResponseStream ()
       use reader = new StreamReader (stream)
  -    return!  reader.AsyncReadToEnd() }
  +    return!  reader.AsyncReadToEnd() (* method extension via FSharp.PowerPack *) }
   
   let worldBankUrl (functions, props) =
       seq { yield "http://api.worldbank.org"
  
positive.code: 
  let c = pages |> XDocument.Parse |> xnested ["countries";"country"] 
  
  c |> xelem "region" |> xvalue
  
  c |> xelem "incomeLevel" |> xattr "id"
  
  c |> xelem "region" |> xattr "id"
  
  /// System.NullReferenceException, if attribute not exists
  /// c |> xelem "iso2Code" |> xattr "id"
negative.code: // hard coded document namespace
  let wb = "http://www.worldbank.org"
  
  /// unsafe helper functions, should rely on option values
  
  let xattr s (el:XElement) = el.Attribute(XName.Get(s)).Value
  
  let xelem s (el:XContainer) = el.Element((XName.Get(s,wb)))
  