code: function addScriptUrlsByPlaceHolder(html, missingScriptUrls, placeholder) {
    // Add the matched whitespace to the replacement specifier, to ensure
    // inserted script tags are indented to the same level as the placeholder.
    const indentedUrls = Array.from(missingScriptUrls).map((u) => '$1' + u);
    return html.replace(placeholder, indentedUrls.join('\n'));
  }
docs: Replaces a string placeholder with <script> tags.
  
  @param {string} html The HTML, containing the placeholder.
  @param {Array.<string>} missingScriptUrls The list of <script> elements.
  @param {string} placeholder The string to replace.
  @return {string} The substituted HTML.