Index Tags

[mminga]

I searched in the forum but could not find the answer.
My wish is to add the COUNTRY to IndexTags.
For example:
When I open Hip Hop as genre, the country or origin should be selectable.
Genre: Hip Hop then COUNTRY: Senegal to browse through it.
Is it possible to add it?
If so, what is then the special tag?

Thanks in advance for an answer.

Update:
A list of all tags including syntax that are possible would be great. So anyone can select it according to the requirements.