docs: function(content){
                  return _chain.call(this, 'body', content, null, function(content){
                      if(typeof content === 'object'){
                          //support FormData to be sent direclty
                          if( !(content instanceof FormData)){
                              //otherwise encode the object/array to a string
                              try {
                                  content = JSON.stringify(content);
                              } catch(e){
                                  throw new TypeError('Unable to stringify body\'s content : ' + e.name);
                              }
                              this.header('Content-Type', 'application/json');
                          }
                      } else {
                          content = content + ''; //cast
                      }
                      return content;
                  });
              }