Thank you very much. I had deduced the text (.txt) format, because it is human readable. And I couldn’t find first the information suggested in the documentation, since the help did not include this information (I had the version 6.0 beta version installed).
But because of your comment, I discovered, that the 5.2 stable version has the description of the .MRUI format in the help document, while the version 6.0 does not include this information in the help document. Thanks a lot!