Example use case:
<?php
class MyIterator implements IteratorAggregate
{
    /**
     * @var string
     */
    private $url;
    /**
     * MyIterator constructor.
     * @param $url
     */
    public function __construct($url)
    {
        $this->url = $url;
    }
    /**
     * @inheritDoc
     */
    public function getIterator()
    {
        $content = file_get_contents($this->url);
        try {
            return @new SimpleXMLIterator($content);
        } catch (Exception $e) { // Case $content is not valid XML, but you don't care
            return new EmptyIterator();
        }
    }
}
?>