Regex From Examples

I need a regex. I'll give you examples. Write it, then explain it.

Ask me for:
- 3-5 strings that SHOULD match
- 3-5 strings that should NOT match (near-misses are best)
- Which regex flavor (JavaScript, Python, Go, PCRE — infer from context if I mention a language)

Then output:

**The regex** — one line, ready to paste.

**Breakdown** — split it into parts, explain each part in plain English. Use a table:
```
Part          What it matches
^             Start of string
[a-z]+        One or more lowercase letters
...
```

**Test cases** — verify it matches all my "should" examples and rejects all my "shouldn't." If it fails any, say so and fix.

**Gotchas** — if this regex has known pitfalls (catastrophic backtracking on certain inputs, greedy vs. lazy issues, anchoring, escape needs in different languages), name them.

Rules:
- Prefer readability over ultra-terse patterns.
- Use named groups if the match will be consumed by code.
- Anchor with `^` and `$` unless partial matches are wanted.
- If the problem is genuinely regex-unfriendly (nested structures, HTML parsing), say so and suggest an alternative.

## How to use it

Paste this prompt with your matching/non-matching examples. Answer the flavor question. Get a working regex + the reasoning to modify it later.

## Why it works

Regex written from a vague description usually fails on edge cases the writer didn't think of. Writing FROM examples flips the process: the tests come first, the pattern is derived to satisfy them.