Source

File: wp-includes/class-walker-comment.php

public function display_element( $element, &$children_elements, $max_depth, $depth, $args, &$output ) {
		if ( ! $element ) {
			return;
		}

		$id_field = $this->db_fields['id'];
		$id       = $element->$id_field;

		parent::display_element( $element, $children_elements, $max_depth, $depth, $args, $output );

		/*
		 * If at the max depth, and the current element still has children, loop over those
		 * and display them at this level. This is to prevent them being orphaned to the end
		 * of the list.
		 */
		if ( $max_depth <= $depth + 1 && isset( $children_elements[ $id ] ) ) {
			foreach ( $children_elements[ $id ] as $child ) {
				$this->display_element( $child, $children_elements, $max_depth, $depth, $args, $output );
			}

			unset( $children_elements[ $id ] );
		}

	}