docs: function validateRuleOptions(id, options, source) {
    var validateRule = validators.rules[id],
      message;
  
    if (!validateRule) {
      validateRule = schemaValidator(getRuleOptionsSchema(id), { verbose: true });
      validators.rules[id] = validateRule;
    }
  
    if (typeof options === 'number') {
      options = [options];
    }
  
    validateRule(options);
  
    if (validateRule.errors) {
      message = [
        source, ':\n',
        '\tConfiguration for rule "', id, '" is invalid:\n'
      ];
      validateRule.errors.forEach(function(error) {
        if (error.field === 'data["0"]') {  // better error for severity
          message.push(
                      '\tSeverity should be one of the following: 0 = off, 1 = warning, 2 = error (you passed "', error.value, '").\n');
        } else {
          message.push(
                      '\tValue "', error.value, '" ', error.message, '.\n'
                  );
        }
      });
  
      throw new Error(message.join(''));
    }
  }