docs: public CsvReader includeFields(String mask) {
  		boolean[] includedMask = new boolean[mask.length()];
  
  		for (int i = 0; i < mask.length(); i++) {
  			char c = mask.charAt(i);
  			if (c == '1' || c == 'T' || c == 't') {
  				includedMask[i] = true;
  			} else if (c != '0' && c != 'F' && c != 'f') {
  				throw new IllegalArgumentException("Mask string may contain only '0' and '1'.");
  			}
  		}
  
  		return includeFields(includedMask);
  	}