docs: function transformCode(transformFn, code, url) {
    let source;
    if (url != null) {
      source = url;
    } else {
      source = 'Inline Babel script';
      inlineScriptCount++;
      if (inlineScriptCount > 1) {
        source += ' (' + inlineScriptCount + ')';
      }
    }
  
    return transformFn(
      code,
      {
        filename: source,
        ...babelOpts
      }
    ).code;
  }