original_string: protected function marshalScheme($scheme): ? string
      {
          if ( null === $scheme ) {
              return null;
          }
  
          if ( ! is_string($scheme) ) {
              throw new UriException(
                  'Scheme must be a string'
              );
          }
  
          return strtolower($scheme);
      }
code: protected function marshalScheme($scheme): ? string
      {
          if ( null === $scheme ) {
              return null;
          }
  
          if ( ! is_string($scheme) ) {
              throw new UriException(
                  'Scheme must be a string'
              );
          }
  
          return strtolower($scheme);
      }
code_tokens: protected function marshalScheme ( $ scheme ) : ? string { if ( null === $ scheme ) { return null ; } if ( ! is_string ( $ scheme ) ) { throw new UriException ( 'Scheme must be a string' ) ; } return strtolower ( $ scheme ) ; }
docstring: marshals the scheme.
  
  @param $scheme
  @return null|string
  @throws UriException
docstring_tokens: marshals the scheme .