function tagOpenBetween(code) {
    if (code === codes.slash) {
      effects.consume(code)
      return end
    }

    // ASCII alphabetical and `:` and `_`.
    if (code === codes.colon || code === codes.underscore || asciiAlpha(code)) {
      effects.consume(code)
      return tagOpenAttributeName
    }

    if (markdownLineEnding(code)) {
      returnState = tagOpenBetween
      return lineEndingBefore(code)
    }

    if (markdownSpace(code)) {
      effects.consume(code)
      return tagOpenBetween
    }

    return end(code)
  }
In opening tag, after tag name.

```markdown
> | a <b> c
        ^
```

@type {State}