code: function createAmpCustomElementTag(tagName, version) {
    const scriptType = AMP_SCRIPT_TYPE_MAP[tagName] || 'custom-element';
    return `<script async ${scriptType}="${tagName}" ` +
        `src="https://cdn.ampproject.org/v0/${tagName}-${version}.js"></script>`;
  }
docs: Builds a script tag for a custom element.
  
  @param {string} tagName The custom element to include.
  @param {number} version The version number to include.
  @return {string} The <script> tag.