wp-includes/class-wp-speculation-rules.php:290Checks whether the given speculation rules source is valid.
$sourcestringbool public static function is_valid_source( string $source ): bool { return isset( self::$source_allowlist[ $source ] ); }Introduced in 6.8.0. Unchanged from 6.8.8 through 7.1.0.
Signature, return type and hooks compared across 4 parsed releases.
src/wp-includes/class-wp-speculation-rules.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.