whole_func_string: function writeTop(d, loc) {
              if (d.indexOf('\n') != -1) {
                  throw 'Can not write content having \\n'
              }
              this.chunks.unshift(chunk(d, loc))
          }
func_code_string: function writeTop(d, loc) {
              if (d.indexOf('\n') != -1) {
                  throw 'Can not write content having \\n'
              }
              this.chunks.unshift(chunk(d, loc))
          }
func_documentation_string: unshift a new chunk