Docs from working code

Generate documentation for this code. Useful, not decorative.

```{{language}}
{{paste code, function, or module}}
```

Audience: {{who reads this — junior on team, external API consumer, future me?}}

Output sections (skip any that don't apply):
1. **What it does** — one sentence, no marketing
2. **When to use it** — and when NOT to (link to alternative if there is one)
3. **Quick example** — the simplest realistic call, with sample input and output
4. **Parameters** — table format, only ones non-obvious from the type signature
5. **Common pitfalls** — what trips people up
6. **What it doesn't do** — explicit non-goals

Skip:
- "This function takes X and returns Y" (that's the signature, the reader can read)
- "Powerful and flexible" or other marketing words
- Examples that are obvious from the function name

If there's no real reason to document this beyond the type signature, tell me and stop.