function tagOpenAttributeName(code) {
    // ASCII alphabetical and `-`, `.`, `:`, and `_`.
    if (
      code === codes.dash ||
      code === codes.dot ||
      code === codes.colon ||
      code === codes.underscore ||
      asciiAlphanumeric(code)
    ) {
      effects.consume(code)
      return tagOpenAttributeName
    }

    return tagOpenAttributeNameAfter(code)
  }
In attribute name.

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

@type {State}