function tagOpen(code) {
    // ASCII alphanumerical and `-`.
    if (code === codes.dash || asciiAlphanumeric(code)) {
      effects.consume(code)
      return tagOpen
    }

    if (
      code === codes.slash ||
      code === codes.greaterThan ||
      markdownLineEndingOrSpace(code)
    ) {
      return tagOpenBetween(code)
    }

    return nok(code)
  }
After `<x`, in opening tag name.

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

@type {State}