My specialty is piano accompaniments.
My lead-in to opening this specific thread
is in my earlier thread,
"My first performance in thirty years."

I played piano in a little chamber ensemble,
as documented in that thread,
which turned Schubert's Trout Quintet
into a Trout Quartet (we lacked a string bass).
Then our violinist went back to university for fall semester,
and what we had left was a Trout Trio.
At the same time, we were making music with a chorus director
who sings baritone and bass-baritone voice.

Because our Trout Trio still has
a piano (me) and a viola (my colleague here),
it was the baritone singer's idea that
we should look at the Brahms Viola Lieder.

(We left the cello to fend for himself.)

So I am playing Brahms's piano accompaniment
while my friend plays the viola
and the chorus director sings the vocal part.

I ought to look further at the research and writing of others
to see if they have traced,
in the singer's melody composed by Brahms,
something derived from traditional/folk sources in the melody.

All I am personally aware of is
that the viola part has that folksong melody in it,
which the viola normally plays when as a solo,
when the singer is silent.