code: function () {
          if (!this.count()) { return 0; }
  
          var raw = this.reduce(function (acc, header) {
              // unparse header only if it has a valid key and is not disabled
              if (header && !header.disabled) {
                  // *( header-field CRLF )
                  acc += Header.unparseSingle(header) + CRLF;
              }
  
              return acc;
          }, E);
  
          return raw.length;
      }
docs: Gets size of a list of headers excluding standard header prefix.
  
  @returns {Number}