Code syntax highlighting in Markdown to PDF

# Syntax highlighting

```python
from dataclasses import dataclass

@dataclass
class Shipment:
    reference: str
    mass_kg: float

    def freight(self, rate_per_kg: float) -> float:
        """Freight charge, rounded to the cent."""
        return round(self.mass_kg * rate_per_kg, 2)
```

```typescript
export async function fetchRates(currency: string): Promise<Map<string, number>> {
  const res = await fetch(`https://api.example.com/rates?base=${currency}`);
  if (!res.ok) throw new Error(`rates: ${res.status}`);
  const { rates } = (await res.json()) as { rates: Record<string, number> };
  return new Map(Object.entries(rates));
}
```

```go
func median(xs []float64) float64 {
    sort.Float64s(xs)
    n := len(xs)
    if n%2 == 1 {
        return xs[n/2]
    }
    return (xs[n/2-1] + xs[n/2]) / 2 // even count: mean of the middle pair
}
```

```rust
fn checksum(digits: &str) -> Option<u8> {
    let sum: u32 = digits.bytes().rev().enumerate()
        .map(|(i, b)| (b - b'0') as u32 * if i % 2 == 0 { 3 } else { 1 })
        .sum();
    Some(((10 - sum % 10) % 10) as u8)
}
```

```sql
SELECT region, SUM(units) AS units, AVG(unit_price) AS avg_price
FROM sales
WHERE sold_at >= DATE '2026-01-01'
GROUP BY region
HAVING SUM(units) > 1000
ORDER BY units DESC;
```

```yaml
service: warehouse-sync
schedule: "0 */6 * * *"
retries: 3
regions: [eu-west, ap-south]
```

```bash
#!/usr/bin/env bash
set -euo pipefail
for f in reports/*.md; do
  echo "converting ${f}"
done
```

```json
{ "order": "A-4172", "items": 3, "express": true, "total": 184.5 }
```

A fence without a language tag stays plain mono, and a language the highlighter does not know prints plain as well.