Thanks, things are clearer now. I was not sure how files which are saved from an app which is not “native” and therefore do not set attributes, were handled. When this association of MIME attributes takes place? When the file is created in the filesystem? When I double click on it on the UI? What is the preferred way to create the mime description files to put into the database? (Where the translations of the various descriptions there goes???).
Btw, TeXmacs use its own format (does not depend on TeX in any way, despite of the name…). We use the ‘text/x-texmacs’ string for the mime type of the documents.