Matroska EditionEntry
I use the term "Edition" in the description.
All chapters are always within one Edition and there may be multiple Editions. Likewise, one Edition may be ordered and another may not.
There are currently 3 flags (0=no, 1=yes) for the Edition. However, the Matroska specs are not clearly defined and there are disagreements in dealing with the flags.
EditionFlagOrdered
If this element is set to 1 then the Edition is ordered and uses Ordered Chapters.
EditionFlagHidden
If this element is set to 1 then the Edition is hidden/invisible and no chapter markers are generated for the timeline. Furthermore, a player should NOT "show" this Edition, meaning the user can not see or select this Edition.
EditionFlagDefault
If this element is set to 1 then the Edition is the default Edition and should be preferred by the player.
Unfortunately this element can be found in every Edition and you would have several default Editions. In addition, it has been determined that the EditionFlagHidden element has a "higher" value. As a result, the EditionFlagDefault element is negated in certain settings and a non-default Edition is still the default Edition.
It's all a lot of confusion in my opinion and I suggested the following for the Matroska specs.
The EditionFlagDefault element has to be moved to level 1 and then exists only once and might have to be renamed EditionDefaultUID.
My recommendation for a player
The "first" Edition where the EditionFlagDefault element was found and has the value 1 is the default Edition. This Edition MUST be used even if it is hidden.
Editions selection in the player
A good Matroska player should have a quick-to-reach selection menu for the Editions. Similar to when you can change the audio track or subtitle track.
LAV Splitter has a very good Edition menu.
Test files
There are always two Editions and only the second is ordered and the third chapter is disabled. This lacks 10 seconds of video and you can see more quickly which Edition is being used after starting. I've prepared a few examples for the numerous possibilities that arise through the combinations of Edition flags.
Editsion 1 non-ordered - Edition 2 ordered
The player should play the 1st Edition.
Edition 1 non-ordered - Edition 2 ordered default
The player should play the 2nd Edition.
Edition 1 non-ordered - Edition 2 ordered hidden default
All tested players play the 1st Edition, because the 2nd Edition is hidden. A player should play but the 2nd Edition, because it is the default Edition.
Edition 1 non-ordered hidden - Edition 2 ordered
The player should play the 2nd Edition, because the 1st Edition is hidden.
Edition 1 non-ordered hidden default - Edition 2 ordered default
All tested players play the 2nd Edition, because the 1st Edition is hidden. A player should play but the first Edition, because it is the first default Edition.
Edition Name
Unfortunately, such a subelement is missing in the Edition structure and you have to use the Matroska Tags.
For each Edition a Tag element must be used. In Targets elment, the corresponding UID is entered in the TagEditionUID element (in the XML only EditionUID). In the SimpleTag (in the XML only Simple) the official Matroska tag "TITLE" is entered in the TagName (in the XML only Name) and in the TagString element (in the XML only String) a name is saved for the Edition.