src/vs/editor/contrib/folding/foldingRanges.ts/FoldingRegions/toString
class FoldingRegions:	public toString() {
		let res: string[] = [];
		for (let i = 0; i < this.length; i++) {
			res[i] = `[${this.isCollapsed(i) ? '+' : '-'}] ${this.getStartLineNumber(i)}/${this.getEndLineNumber(i)}`;
		}
		return res.join(', ');
	}