AEM Edge Delivery (helix-sitemap): which per-URL sitemap attributes are supported? Is priority/changefreq possible, and how to serve a sitemap index?

Context: We run an AEM Edge Delivery Services site (repoless, Configuration Service; content authored in AEM). Sitemaps are generated by helix-sitemap. We push the sitemap config to content/sitemap.yaml via the Admin API and generate per-language sitemaps. Multilingual: es, en, pt, fr.

What we've confirmed:

• Per-language <urlset> generation works via a languages map with source: /{lang}/query-index.json.

• <lastmod> is emitted when we add a lastmod format to the config.

• We could not find any way to emit <priority> or <changefreq> per URL, and we don't see them in the config schema.

• helix-sitemap doesn't appear to generate a <sitemapindex> for multilingual — only the per-language <urlset> files.

Questions:

1. Supported per-URL attributes: What sitemap attributes can helix-sitemap emit per URL (<loc>, <lastmod>, <changefreq>, <priority>, hreflang alternates)? Is there a definitive list?

2. priority / changefreq: Is there ANY supported way to include <priority>/<changefreq> per URL (e.g., a query-index property mapped in the sitemap config)? If not, is the official recommendation to omit them (given Google states it ignores them)? A config example either way would help.

3. Sitemap index: Can a <sitemapindex> (referencing the per-language sitemaps) be produced via the sitemap config or the Admin API, or is a static sitemap.xml/sitemap-index.xml the only option? Best practice for a repoless (Configuration Service) site?

4. Example: Could you share a full multilingual sitemap.yaml example that produces an index + per-language sitemaps with lastmod (and priority if at all possible)?