code: function(p) {
      p = p || this.path();
      return (!p || p == "/")? null : p.substring(p.lastIndexOf("/")+1);
    }
docs: SpahQL#keyName() -> String or null
  
  Returns the name for the first item in this set, based on its path. If the item is the root
  or if the result was not created from a path query then the method will return null.
  
  select("/foo").keyName() //-> "foo"
  select("/foo/bar/.size").keyName() // -> ".size"