src/vs/editor/common/model/pieceTreeTextBuffer/rbTreeBase.ts/TreeNode/next
class TreeNode:	public next(): TreeNode {
		if (this.right !== SENTINEL) {
			return leftest(this.right);
		}

		let node: TreeNode = this;

		while (node.parent !== SENTINEL) {
			if (node.parent.left === node) {
				break;
			}

			node = node.parent;
		}

		if (node.parent === SENTINEL) {
			return SENTINEL;
		} else {
			return node.parent;
		}
	}