As usual, you were right.
Now my frame style looks right$if(%_isplaying%,
$set_style(frame-top,1,$get(text-play))
$set_style(frame-bottom,1,$get(text-play)),
$set_style(frame-top,1,
$ifequal($mod(%_playlist_number%,2),0,
$get(back-even),$get(back-odd)))
$set_style(frame-bottom,1,
$ifequal($mod(%_playlist_number%,2),0,
$get(back-even),$get(back-odd)))
)
If you know a simpler way, please let me know.
Thanks.