works_in_php56.php

<?php
$data='<data>
    <seg id="A1"/>
    <seg id="A2"/>
    <seg id="A3"/>
    <seg id="A4"/>
    <seg id="A5"/>
</data>';

$doc=new SimpleXMLElement($data);
$seg_ref = $doc->seg;
unset($seg_ref->{0});

echo $doc->asXml();