wp-includes/class-wp-date-query.php:1062Sanitizes a 'relation' operator.
$relationstringstring public function sanitize_relation( $relation ) { if ( 'OR' === strtoupper( $relation ) ) { return 'OR'; } else { return 'AND'; } }Introduced in 6.0.3. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-date-query.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.