function begin(code) {
    if (code === marker) {
      effects.enter(markerType)
      effects.consume(code)
      effects.exit(markerType)
      effects.exit(type)
      return ok
    }

    effects.enter(stringType)
    return atBreak(code)
  }
After opening marker.

This is also used at the closing marker.

```markdown
> | "a"
     ^
```

@type {State}