original_string: public function addClientHeader(string $headerName, $headerValue): self
      {
          $this->clientConfig['headers'][$headerName] = $headerValue;
          return $this;
      }
code: public function addClientHeader(string $headerName, $headerValue): self
      {
          $this->clientConfig['headers'][$headerName] = $headerValue;
          return $this;
      }
code_tokens: public function addClientHeader ( string $ headerName , $ headerValue ) : self { $ this -> clientConfig [ 'headers' ] [ $ headerName ] = $ headerValue ; return $ this ; }
docstring: add a client request header
  @param string $headerName
  @param mixed $headerValue
  @return self
docstring_tokens: add a client request header