I was investigating the use of alternative translations to prevent auto-propagation, and although it's a little strange to use them for this purpose (instead of a segment status or context menu command to proceed without propagation): they can be used.
Digging deeper, I was wondering how to insert an already defined alternative translation, apart from dragging over it–while it's still visible in the Project segments pane.
And then there's this representation in the TMX file. Does the current TMX 1.x implementation of CafeTran allow storage of alternative translations? Or is this something for TMX 2?
Step 1: Obviously it's possible to add alternative facts to SDLXLIFF projects too:
On reopening the SDLXLIFF in CafeTran, I noticed that the alternative translation has disappeared.
Alternative translations are not stored in TMX memories and I don't know if sdlxliff supports standard xliff alternative translations.
The current solution to block automatic propagation via alternative translations may be replaced by "no propagate" segment status in the future.