code: public Schema withRule(IValidationRule rule) {
  		_rules = _rules != null ? _rules : new ArrayList<IValidationRule>();
  		_rules.add(rule);
  		return this;
  	}
docs: Adds validation rule to this schema.
  
  This method returns reference to this exception to implement Builder pattern
  to chain additional calls.
  
  @param rule a validation rule to be added.
  @return this validation schema.