Indexable Sitemap improvements

[BobBreukhoven]

https://yoast.atlassian.net/browse/FIX-20

Changes that indexable-based sitemaps introduce:

• Users get significantly faster page load times when loading sitemap pages
• Visitors (and search engines) get redirected to the WordPress Core sitemaps that were released with WP 5.5 when they go to any Yoast SEO sitemap page the site isn’t fully indexed yet. Indexing a site can be achieved by:
  • Clicking the Start SEO data optimization button.
  • For sites with fewer than 25 post+terms+users combined, visiting the Yoast SEO admin pages once if WP-Cron is disabled.
  • Waiting for the background indexing to complete. we index 15 posts/terms/users every 15 minutes using WP-Cron if WP-Cron is not disabled.
• images don’t list their alt attribute in the sitemaps anymore. According to Joost, search engines don’t look at the alt text in the sitemaps, as they will generally just visit the page that the image belongs to and note the alt text there.
• The $links or $url in any sitemap filter no longer have a chf and pri keys. They weren’t used and were only there for backwards compatibility reasons. The affected filters are:
  • wpseo_sitemap_url
  • wpseo_sitemap_entry
• A bug has been fixed where the timestamps of a link in the sitemap index wasn’t always showing the most recent modification date of all items in that sitemap, but would instead show the second or third most recent modification date. As far as we know, this doesn’t impact SEO, as the modification date on the sitemap index did change when a new post was published, causing search engines to revisit the sitemap.
• Removed hooks:
  • wpseo_hit_sitemap_index
  • wpseo_sitemap_exclude_empty_terms and wpseo_sitemap_exclude_empty_terms_taxonomy
• Added a third parameter to the wpseo_sitemap_entry hook: the WordPress object ID (which is the post id, term id or user id)

[BobBreukhoven]

We need to have a look at the Jira ticket and see what is already done and what is still needed

[jonoalderson]

Before diving too deep into this, we should make a decision on whether we should pursue a combined XML sitemap model, instead of having different outputs for different content formats.

Practically, this would mean making our XML sitemaps filter our main XML sitemap behaviour, instead of producing its own output. There'd likely be other technical considerations and changes, and changes to our existing product/marketing narrative (and a need to redirect legacy links).

See https://developers.google.com/search/docs/crawling-indexing/sitemaps/combine-sitemap-extensions for spec. See https://yoast.slack.com/archives/C02CDFDA5/p1676432351194149 for context.