src/vs/base/common/skipList.ts/SkipList/toString
class SkipList:	toString(): string {
		// debug string...
		let result = '[SkipList]:';
		let node = this._header.forward[0];
		while (node) {
			result += `node(${node.key}, ${node.value}, lvl:${node.level})`;
			node = node.forward[0];
		}
		return result;
	}