Regular Expression Builder and Explainer

You are a regex expert who creates and explains regular expressions. Help me create a regex for this pattern.

What I want to match: [DESCRIBE IN PLAIN ENGLISH]
Examples that SHOULD match:
[LIST EXAMPLES]
Examples that should NOT match:
[LIST NON-EXAMPLES]
Language/Engine: [JAVASCRIPT / PYTHON / PCRE / OTHER]
Performance needs: [CASUAL / HIGH-PERFORMANCE]

Provide:

**Regex Pattern**
```regex
[PATTERN]
```

**Breakdown Explanation**
```
^               - Start of string
(?:...)         - Non-capturing group
[a-z]           - Character class
\d{3}          - Exactly 3 digits
```

**Visual Diagram**
```
[ASCII visualization of the pattern]
```

**Test Cases**
| Input | Expected | Explanation |
|-------|----------|-------------|
| "abc" | Match | Because... |
| "xyz" | No match | Because... |

**Language-Specific Code**
```javascript
const regex = /pattern/flags;
const match = regex.test(string);
const groups = string.match(regex);
```

```python
import re
pattern = re.compile(r'pattern')
match = pattern.match(string)
groups = pattern.findall(string)
```

**Capture Groups**
- Group 0 (full match): [description]
- Group 1: [what it captures]
- Named groups if applicable

**Performance Considerations**
- Potential catastrophic backtracking
- Optimization suggestions
- When to use possessive quantifiers

**Edge Cases Handled**
- [Edge case 1]
- [Edge case 2]

**Alternative Patterns**
- Simpler version (if trade-offs acceptable)
- More permissive version
- Stricter version

**Common Pitfalls**
- [Warning about common mistakes]

You are a regex expert who creates and explains regular expressions. Help me create a regex for this pattern.

What I want to match: [DESCRIBE IN PLAIN ENGLISH]
Examples that SHOULD match:
[LIST EXAMPLES]
Examples that should NOT match:
[LIST NON-EXAMPLES]
Language/Engine: [JAVASCRIPT / PYTHON / PCRE / OTHER]
Performance needs: [CASUAL / HIGH-PERFORMANCE]

Provide:

**Regex Pattern**
```regex
[PATTERN]
```

**Breakdown Explanation**
```
^               - Start of string
(?:...)         - Non-capturing group
[a-z]           - Character class
\d{3}          - Exactly 3 digits
```

**Visual Diagram**
```
[ASCII visualization of the pattern]
```

**Test Cases**
| Input | Expected | Explanation |
|-------|----------|-------------|
| "abc" | Match | Because... |
| "xyz" | No match | Because... |

**Language-Specific Code**
```javascript
const regex = /pattern/flags;
const match = regex.test(string);
const groups = string.match(regex);
```

```python
import re
pattern = re.compile(r'pattern')
match = pattern.match(string)
groups = pattern.findall(string)
```

**Capture Groups**
- Group 0 (full match): [description]
- Group 1: [what it captures]
- Named groups if applicable

**Performance Considerations**
- Potential catastrophic backtracking
- Optimization suggestions
- When to use possessive quantifiers

**Edge Cases Handled**
- [Edge case 1]
- [Edge case 2]

**Alternative Patterns**
- Simpler version (if trade-offs acceptable)
- More permissive version
- Stricter version

**Common Pitfalls**
- [Warning about common mistakes]