Great thread! Long live the original musical instrument!
Yes, thank you, Moulden, for a good synopsis of a capella tenets.
Bits of a capella continue in the USA, though out of the limelight.
I ran a regular Celtic-song workshop in Southern Calif for years.
The main rule was, no instruments!
The group learned tunes and words, and were advised that once they learned a song *as a song*, it was then theirs to perform as they wished.
I think I had good results in spreading the trad gospel.
(Thinking of starting it up again someday!)
Rock on, vocalists, and simply be honest with your material.