Storing multiple values in the same tag

[Bunbury]

Hi,

What is the syntax for storing multiple values in the same tag ?
For example if I have a concerto for Violin AND Piano, and I stor this information in the tag SolistInstrument, what should I store ? "Violin,Piano" or "Violin;Piano" or something else entirely ?

Maybe it depends on the controller ? Is this case, what about the main ones on ios and android ? How do I make this work ?

The behaviour I would like to see is that a song that has two values for a tag appears in both filters. The concerto would appear when I choose Violin but also when I choose Piano. And I don't want a third value being Violin and Piano.

Can you guys help ?

** EDIT

Let me rephrase the questions
Apparently the correct way is to store twice the same tag in the file, with two different values.
MinimServer reads these and send an XML file to the controller who will display them.
There is an option to minim to choose how to send the XML file (I guess the correct setting depends on what controller you're using)
So my question becomes: how do I make sure the file is properly tagged for Minim ?
I'm using MP3TAG and the interface does not allow this. Some posts suggest using \\ in the field but then it won't be stored in the file as multiple entries...
Help