function sequenceOpen(code) {
    if (code === marker) {
      sizeOpen++
      effects.consume(code)
      return sequenceOpen
    }

    if (sizeOpen < constants.codeFencedSequenceSizeMin) {
      return nok(code)
    }

    effects.exit(types.codeFencedFenceSequence)
    return markdownSpace(code)
      ? factorySpace(effects, infoBefore, types.whitespace)(code)
      : infoBefore(code)
  }
In opening fence sequence.

```markdown
> | ~~~js
     ^
  | alert(1)
  | ~~~
```

@type {State}