code: public function checkPermission()
  	{
  		if ($this->User->isAdmin)
  		{
  			return;
  		}
  
  		// Check the theme import and export permissions (see #5835)
  		switch (Contao\Input::get('key'))
  		{
  			case 'importTheme':
  				if (!$this->User->hasAccess('theme_import', 'themes'))
  				{
  					throw new Contao\CoreBundle\Exception\AccessDeniedException('Not enough permissions to import themes.');
  				}
  				break;
  
  			case 'exportTheme':
  				if (!$this->User->hasAccess('theme_import', 'themes'))
  				{
  					throw new Contao\CoreBundle\Exception\AccessDeniedException('Not enough permissions to export themes.');
  				}
  				break;
  		}
  	}
docs: Check permissions to edit the table
  
  @throws Contao\CoreBundle\Exception\AccessDeniedException