propertycollection.php

См. документацию.

<?php
 
namespace Bitrix\Calendar\Core\Base;
 
abstract class PropertyCollection extends Collection implements Property
{
    public function __toString()
    {
        return $this->toString();
    }

    public function getFields(): array
    {
        return [
            'collection' => $this->collection,
        ];
    }

    public function toString(string $separator = ', '): string
    {
        return implode($separator, $this->collection);
    }
}