player.html

<script src="https://cdnjs.cloudflare.com/ajax/libs/tone/13.8.12/Tone.js"></script>
<textarea id="foo" style="width: 100%; height: 100%;">this track continues into the new line &
here
but this is a different track playing simultaneously with first.</textarea>
<script>;(function(){

foo.onmouseup = function(){ play(foo.value) }

window.play = function play(S){
	var N = [], f = true;
	S = split(S, '\n\n'); // split song into sections if haven't already
	S.forEach(function(s, T){
		if(!f){ return N.push(s) } f = false; // handle recurse
		if(typeof s == 'string'){ s = s.replace('&\n', '') } // parse once
		var n = []; // do we have next?
		T = split(s, '\n');
		T.forEach(function(t){ // For each track, of the first section, of the current version of the song
			new Tone.Synth().toMaster().triggerAttackRelease(convert(t[0])+'4', '0.1s'); // ... play the first note of each track!
			t = t.slice(1); if(t.length){ n.push(t) } // handle recurse
		});
		if(n.length){ N.push(n) }
	});
	if(N.length){ setTimeout(function(){ play(N) }, 100) }
}
function convert(t){
	var notes = 'ABCDEFG'.split('');
	return notes[t.charCodeAt(0) % notes.length]
}
function split(t, on){
 return typeof t == 'string'? t.split(on) : t;
}

}());</script>