The volume level, between 0 and 100, to which to adjust a previously defined background mp3 file (see <bg_mp3 file=""/>) and the number of seconds the volume transition should take.
Note that any subsequently defined background mp3 file will begin playing at the most recently set volume level.
Child of: <click>, <drag_drop>, <drag_move>, <mouse_click>, <mouse_down>, <mouse_move>, <mouse_out>, <mouse_over>, <node name="">, <press>, <release>
Parent of: Nothing
Example:
<bg_mp3 toLevel="75" seconds="5"/>