How to use the @microsoft/tsdoc.StringBuilder function in @microsoft/tsdoc

private _renderMarkdown(docSection: DocSection, contextApiItem: ApiItem): string {
    const stringBuilder: StringBuilder = new StringBuilder();

    this._markdownEmitter.emit(stringBuilder, docSection, {
      contextApiItem,
      onGetFilenameForApiItem: (apiItem: ApiItem) => {
        // NOTE: GitHub's markdown renderer does not resolve relative hyperlinks correctly
        // unless they start with "./" or "../".
        return `xref:${this._getUid(apiItem)}`;
      }
    });

    return stringBuilder.toString().trim();
  }

case ApiItemKind.PropertySignature:
        break;
      case ApiItemKind.TypeAlias:
        break;
      case ApiItemKind.Variable:
        break;
      default:
        throw new Error('Unsupported API item kind: ' + apiItem.kind);
    }

    if (appendRemarks) {
    this._writeRemarksSection(output, apiItem);
    }

    const filename: string = path.join(this._outputFolder, this._getFilenameForApiItem(apiItem));
    const stringBuilder: StringBuilder = new StringBuilder();

    stringBuilder.append('\n\n');

    this._markdownEmitter.emit(stringBuilder, output, {
      contextApiItem: apiItem,
      onGetFilenameForApiItem: (apiItemForFilename: ApiItem) => {
        return this._getLinkFilenameForApiItem(apiItemForFilename);
      }
    });

    let pageContent: string = stringBuilder.toString();

    if (this._pluginLoader.markdownDocumenterFeature) {
      // Allow the plugin to customize the pageContent
      const eventArgs: IMarkdownDocumenterFeatureOnBeforeWritePageArgs = {
        apiItem: apiItem,

let exampleNumber: number = 1;
        for (const exampleBlock of exampleBlocks) {
          const heading: string = exampleBlocks.length > 1 ? `Example ${exampleNumber}` : 'Example';

          output.appendNode(new DocHeading({ configuration: this._tsdocConfiguration, title: heading }));

          this._appendSection(output, exampleBlock.content);

          ++exampleNumber;
        }
      }
    }

    const filename: string = path.join(this._outputFolder, this._getFilenameForApiItem(apiItem, true));
    const stringBuilder: StringBuilder = new StringBuilder();

    this._markdownEmitter.emit(stringBuilder, output, {
      contextApiItem: apiItem,
      onGetFilenameForApiItem: (apiItemForFilename: ApiItem) => {
        return this._getLinkFilenameForApiItem(apiItemForFilename);
      },
    });

    FileSystem.writeFile(filename, stringBuilder.toString(), {
      convertLineEndings: NewlineKind.CrLf,
    });
  }

public getModifiedText(): string {
    const output: StringBuilder = new StringBuilder();

    this._writeModifiedText({
      output,
      separatorOverride: undefined
    });

    return output.toString();
  }