code: protected function isValidOption($varInput)
  	{
  		if ($varInput == '')
  		{
  			return true;
  		}
  
  		foreach ($this->arrAvailableOptions as $strGroup=>$arrValues)
  		{
  			if ($strGroup == 'image_sizes')
  			{
  				if (isset($arrValues[$varInput]))
  				{
  					return true;
  				}
  			}
  			elseif (\in_array($varInput, $arrValues))
  			{
  				return true;
  			}
  		}
  
  		return false;
  	}
docs: Check whether an input is one of the given options
  
  @param mixed $varInput The input string or array
  
  @return boolean True if the selected option exists