getItem(document, track, index) {
		let i = 0;
		const entries = track.childNodes;
		for (let entry of entries) {
			// Skip blank
			if (entry.tagName === 'blank') {
				// continue;
			}
			// Simple entry
			else if (new RegExp(/^producer/).test(entry.getAttribute('producer'))) {
				if (i === index) {
					return entry;
				}
				i++;
			}
			// Container of entries
			else {
				const tractor = document.getElementById(entry.getAttribute('producer'));
				const tracks = tractor.getElementsByTagName('multitrack').item(0).childNodes;
				for (let track of tracks) {
					if (i === index) {
						return track;
					}
					i++;
				}
			}
		}
		return null;
	}
Get NTH element of playlist - entry (for simple) / track (for complex)

@param {Document} document
@param {Element} track
@param {Number} index
@return {?Element}