original_string: public function addNamespace($prefix, $uri)
      {
          if (empty($prefix))
              throw new \InvalidArgumentException('The prefix may not be emtpy or NULL.');
          if (empty($uri))
              throw new \InvalidArgumentException('The uri may not be empty or NULL.');
  
          $this->namespaces[$prefix] = $uri;
  
          return $this;
      }
code: public function addNamespace($prefix, $uri)
      {
          if (empty($prefix))
              throw new \InvalidArgumentException('The prefix may not be emtpy or NULL.');
          if (empty($uri))
              throw new \InvalidArgumentException('The uri may not be empty or NULL.');
  
          $this->namespaces[$prefix] = $uri;
  
          return $this;
      }
code_tokens: public function addNamespace ( $ prefix , $ uri ) { if ( empty ( $ prefix ) ) throw new \ InvalidArgumentException ( 'The prefix may not be emtpy or NULL.' ) ; if ( empty ( $ uri ) ) throw new \ InvalidArgumentException ( 'The uri may not be empty or NULL.' ) ; $ this -> namespaces [ $ prefix ] = $ uri ; return $ this ; }
docstring: Add a XML namespace to the internal list of namespaces. After that,
  custom channel elements can be used properly to generate a valid feed.
  
  @access   public
  @param    string $prefix namespace prefix
  @param    string $uri namespace name (URI)
  @return   self
  @link     http://www.w3.org/TR/REC-xml-names/
  @throws   \InvalidArgumentException if the prefix or uri is empty or NULL.
docstring_tokens: Add a XML namespace to the internal list of namespaces . After that custom channel elements can be used properly to generate a valid feed .