code: public function createFileList($strFilter='', $filemount=false)
  	{
  		// Deprecated since Contao 4.0, to be removed in Contao 5.0
  		if ($strFilter === true)
  		{
  			@trigger_error('Passing "true" to Backend::createFileList() has been deprecated and will no longer work in Contao 5.0.', E_USER_DEPRECATED);
  
  			$strFilter = 'gif,jpg,jpeg,png';
  		}
  
  		$this->import(BackendUser::class, 'User');
  
  		if ($this->User->isAdmin)
  		{
  			return $this->doCreateFileList(Config::get('uploadPath'), -1, $strFilter);
  		}
  
  		$return = '';
  		$processed = array();
  
  		// Set custom filemount
  		if ($filemount)
  		{
  			$this->User->filemounts = array($filemount);
  		}
  
  		// Limit nodes to the filemounts of the user
  		foreach ($this->eliminateNestedPaths($this->User->filemounts) as $path)
  		{
  			if (\in_array($path, $processed))
  			{
  				continue;
  			}
  
  			$processed[] = $path;
  			$return .= $this->doCreateFileList($path, -1, $strFilter);
  		}
  
  		return $return;
  	}
docs: Get all allowed files and return them as string
  
  @param string  $strFilter
  @param boolean $filemount
  
  @return string