Mistake: nesting sitemap index files inside each other

Mistake: nesting sitemap index files inside each other

A sitemap index can only point to sitemaps. It cannot point to another index. Two-level nesting is invalid and the deeper files go uncrawled silently.

Fix checklist:
— ✅ The index file lists only leaf sitemaps, never another <sitemapindex>
— ✅ Maximum 50,000 sitemap entries in one index, max 50MB uncompressed
— Need more than 50,000 child sitemaps? You have a URL-count problem to solve upstream, not a nesting one
— Each child <loc> is an absolute URL on the same host as the index

Definition of done: open the index, confirm every entry is a .xml sitemap (not an index), and that the total covered URL count matches your real indexable page count within 2%.