src/vs/workbench/api/common/extHostTypes.ts/DocumentLink/constructor
class DocumentLink:	constructor(range: Range, target: URI | undefined) {
		if (target && !(URI.isUri(target))) {
			throw illegalArgument('target');
		}
		if (!Range.isRange(range) || range.isEmpty) {
			throw illegalArgument('range');
		}
		this.range = range;
		this.target = target;
	}