src/vs/workbench/api/common/extHostTypes.ts/Selection/isSelection
class Selection:	static isSelection(thing: any): thing is Selection {
		if (thing instanceof Selection) {
			return true;
		}
		if (!thing) {
			return false;
		}
		return Range.isRange(thing)
			&& Position.isPosition((<Selection>thing).anchor)
			&& Position.isPosition((<Selection>thing).active)
			&& typeof (<Selection>thing).isReversed === 'boolean';
	}