wp-includes/comment.php:3481Rejects incoming trackbacks in non-production environments.
function wp_maybe_disable_trackback_for_environment() { if ( wp_should_disable_pings_for_environment() ) { trackback_response( 1, __( 'Trackbacks are disabled in non-production environments.' ) ); }}Introduced in 7.1.0.
Signature, return type and hooks compared across 1 parsed release.
src/wp-includes/comment.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.