function numeric(code) {
    if (code === codes.uppercaseX || code === codes.lowercaseX) {
      effects.enter(types.characterReferenceMarkerHexadecimal)
      effects.consume(code)
      effects.exit(types.characterReferenceMarkerHexadecimal)
      effects.enter(types.characterReferenceValue)
      max = constants.characterReferenceHexadecimalSizeMax
      test = asciiHexDigit
      return value
    }

    effects.enter(types.characterReferenceValue)
    max = constants.characterReferenceDecimalSizeMax
    test = asciiDigit
    return value(code)
  }
After `#`, at `x` for hexadecimals or digit for decimals.

```markdown
> | a&#123;b
       ^
> | a&#x9;b
       ^
```

@type {State}