In Tuleap 12.5, we introduced the ability to use a new "commonmark"
format for follow-up comments. However, this format is not recognized by XML import / export and considered invalid. It means that if you export a Tracker with comments in "commonmark"
format, you will not be able to import it again because the XML import check will reject the "commonmark"
format as being invalid.
We should fix this and allow "commonmark"
format to be imported and exported correctly.
Issue introduced (again) by git #tuleap/stable/a0ed87fa219948f67ecaf3d86ad5b928c3c8bb31