anchor.diff:    /// ```
     ///
     /// The primary language subtag must not be null. The region subtag is
  -  /// optional.
  +  /// optional. When there is no region/country subtag, the parameter should
  +  /// be omitted or passed `null` instead of an empty-string.
     ///
     /// The subtag values are _case sensitive_ and must be one of the valid
     /// subtags according to CLDR supplemental data:
  
positive.code: ///    [Locale].
  class Locale {
    /// Creates a new Locale object. The first argument is the
    /// primary language subtag, the second is the region subtag.
    ///
    /// For example:
    ///
  
negative.code:   /// [script](http://unicode.org/cldr/latest/common/validity/script.xml) and
    /// [region](http://unicode.org/cldr/latest/common/validity/region.xml) for
    /// each of languageCode, scriptCode and countryCode respectively.
    ///
    /// The [countryCode] subtag is optional. When there is no country subtag,
    /// the parameter should be omitted or passed `null` instead of an empty-string.
    ///
    /// Validity is not checked by default, but some methods may throw away
    /// invalid data.
  