code: public function offsetSet( $attributeName, $attribute )
      {
          if ( !is_string( $attributeName ) ||
               !is_string( $attribute ) )
          {
              // We only accept strings for name AND content
              throw new ValueException( $attribute, 'string' );
          }
  
          $this->attributes[$attributeName] = $attribute;
      }
docs: Set attribute value acceesd through array access
  
  Set attribute value acceesd through array access
  
  @param string $attributeName
  @param string $attribute
  @return void