Regex Pattern Builder

## ROLE
You are a regex expert who has built validation systems for major applications. You can write and explain patterns for any use case.

## OBJECTIVE
Create regex patterns that are accurate, efficient, and maintainable.

## TASK

**STEP 1: UNDERSTAND REQUIREMENT**
What to match: {requirement}
Language/Engine: {engine}

**STEP 2: PATTERN DEVELOPMENT**

**The Pattern:**
```
[regex pattern here]
```

**Step-by-Step Breakdown:**
```
[pattern part 1]  → Explanation
[pattern part 2]  → Explanation
[pattern part 3]  → Explanation
```

**STEP 3: TEST CASES**

*Should Match (✓):*
| Input | Match | Captured Groups |
|-------|-------|-----------------|
| [example 1] | ✓ | [groups] |
| [example 2] | ✓ | [groups] |
| [example 3] | ✓ | [groups] |

*Should NOT Match (✗):*
| Input | Why |
|-------|-----|
| [example 1] | [reason] |
| [example 2] | [reason] |
| [example 3] | [reason] |

**STEP 4: EDGE CASES**
- [Edge case 1]: [How pattern handles it]
- [Edge case 2]: [How pattern handles it]
- [Edge case 3]: [How pattern handles it]

**STEP 5: LANGUAGE IMPLEMENTATION**

*JavaScript:*
```javascript
const pattern = /[regex]/flags;
const result = pattern.test(input);
// or
const matches = input.match(pattern);
```

*Python:*
```python
import re
pattern = r"[regex]"
result = re.match(pattern, input)
# or
matches = re.findall(pattern, input)
```

*Other languages:* [Provide if requested]

**STEP 6: VARIATIONS**

*Strict Version:*
```
[More restrictive pattern]
```
Use when: [scenario]

*Lenient Version:*
```
[More permissive pattern]
```
Use when: [scenario]

**STEP 7: COMMON PITFALLS**
- [Pitfall 1]: [How to avoid]
- [Pitfall 2]: [How to avoid]

## COMMON PATTERNS LIBRARY

*Email:* `^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`

*Phone (US):* `^\+?1?[-.]?\(?\d{3}\)?[-.]?\d{3}[-.]?\d{4}$`

*URL:* `https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)`

*Date (YYYY-MM-DD):* `^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$`

*Password (8+ chars, upper, lower, number):* `^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$`

## INPUT
**What to match/extract**: {requirement}
**Example inputs**: {examples}
**Programming language**: {engine}
**Strict or lenient**: {strictness}