extensions/typescript-language-features/src/languageFeatures/completions.ts/MyCompletionItem/getDetails
class MyCompletionItem:	private getDetails(
		client: ITypeScriptServiceClient,
		detail: Proto.CompletionEntryDetails,
	): string | undefined {
		const parts: string[] = [];

		if (detail.kind === PConst.Kind.script) {
			// details were already added
			return undefined;
		}

		for (const action of detail.codeActions ?? []) {
			parts.push(action.description);
		}

		parts.push(Previewer.plainWithLinks(detail.displayParts, client));
		return parts.join('\n\n');
	}