src/vs/workbench/contrib/notebook/browser/contrib/fold/foldingModel.ts/FoldingModel/getRegionAtLine
class FoldingModel:	getRegionAtLine(lineNumber: number): FoldingRegion | null {
		if (this._regions) {
			let index = this._regions.findRange(lineNumber);
			if (index >= 0) {
				return this._regions.toRegion(index);
			}
		}
		return null;
	}