code: function stringToBoolean(string) {
  	if (typeof string === 'boolean') {
  		// nothing to do, just return
  		return string;
  	} else if (typeof string === 'number') {
  		if (string === 0) {
  			return false;
  		}
  
  		if (string === 1) {
  			return true;
  		}
  	} else if (typeof string === 'string') {
  		var trueValues = ['Y', 'J', 'T', 'JA', 'TRUE', 'YES', '1', 'S', 'SI'];
  		var falseValues = ['N', 'F', 'NEIN', 'FALSE', 'NO', '0'];
  		if (isElementInList(string, trueValues)) {
  			return true;
  		} else if (isElementInList(string, falseValues)) {
  			return false;
  		}
  	}
  
  	return undefined;
  }
docs: /*
  Convert a value to a boolean value by comparing the upper case version
  of this string to a list of true and false values.
  If the given string is neither false-ish nor true-ish, null is returned.
  @param string the string to check.
  @return true or false, if the string is a true-ish or false-ish value
  respectiveley. Null otherwise.