# AUR4105

## Error Message

`AUR4105: Unsupported rule {{ruleName}}`

## Description

This error occurs when attempting to hydrate a validation rule that is not recognized or supported by the current validation system. This can happen when:

1. Using custom rules that weren't registered
2. Deserializing rules from a different validation library
3. Rule names have changed between versions
4. Typos in rule names

## Common Scenarios

```typescript
// ❌ Problem: Unsupported rule name
const rules = [{
  property: 'age',
  rules: [{ name: 'isPositiveInteger' }] // Custom rule not registered
}];
```

## Solution

```typescript
// ✅ Correct: Register custom rules first
import { ValidationRules } from '@aurelia/validation';

// Register custom rule
ValidationRules.customRule(
  'isPositiveInteger',
  (value) => value > 0 && Number.isInteger(value),
  'Value must be a positive integer'
);

// Now the rule can be hydrated
validationRules.hydrateRules(rules);
```