Feature request: index value formatting

[ruckmann]

I just double-checked the topic by doing the following:
- I added a new index tag "test" to my index tag list containing a tag "composer" (among others) and inserted it at the beginning of the list.
- I added a tagValue instruction test.indexValue={composer} (first tagValue instruction of the instruction list)
Result: composer has a valid tag value, test remains empty (no tag)

I think, this is an simple test case you could double-check on your side as well.

B.t.w. the version I am working with is 0.8.3.