The eXtensible Application Markup Language(XAML) is declaritive XML-based markup language develop by Microsoft for creating a rich graphical user interface(GUI). XAML language is the native RadRichTextEditor document format.
Since R2 2023 SP1 the XamlFormatProvider automatically verifies the imported XAML. More information is available in the Xaml Verification article.
XamlFormatProvider is compliant with the XAML markup language.