[TremiDkhar]

Sitemap providers registered with a name containing a dash, such as wp_register_sitemap_provider( 'custom-plugin', $provider ), are listed in the sitemap index, but their URL shows the home page instead of the sitemap.

The rewrite rules only match [a-z] for the provider name, so wp-sitemap-custom-plugin-1.xml is parsed as provider custom with object subtype plugin. Names with digits or underscores don't match at all.

This PR:

• Widens the provider part of the sitemap rewrite rules to [a-z\d_-].
• In WP_Sitemaps::render_sitemaps(), when the parsed provider and subtype don't match a registered provider, matches the full route against the registered provider names.

Core sitemaps (posts, taxonomies, users) are parsed as before.

Testing Instructions

1. Add this mu-plugin and flush permalinks:

   <?php
   add_filter( 'wp_sitemaps_enabled', '__return_true' );
   add_action( 'init', static function () {
    $provider = new class() extends WP_Sitemaps_Provider {
     public function __construct() {
      $this->name        = 'custom-plugin';
      $this->object_type = 'custom';
     }
     public function get_url_list( $page_num, $object_subtype = '' ) {
      return array( array( 'loc' => home_url( '/custom-url/' ) ) );
     }
     public function get_max_num_pages( $object_subtype = '' ) {
      return 1;
     }
    };
    wp_register_sitemap_provider( 'custom-plugin', $provider );
   } );

2. Open /wp-sitemap.xml and click the wp-sitemap-custom-plugin-1.xml link.

3. Before the patch: the theme's 404 page is shown. After the patch: the sitemap lists /custom-url/.

4. Check that /wp-sitemap-posts-post-1.xml still works.

Unit tests can be added once the approach is agreed on.

Trac ticket: https://core.trac.wordpress.org/ticket/51280

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5.5
Used for: Investigating the bug, drafting the fix and this description; the final change was reviewed and edited by me.

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