- simplexml_load_string: documentation ( source)
<?php
$x = <<<XML
<data type="current observations">
<time-layout time-coordinate="local">
<start-valid-time period-name="current">2013-05-27T13:53:00-04:00</start-valid-time>
</time-layout>
</data>
XML;
$weather = simplexml_load_string($x);
$data = $weather->xpath("/data[@type='current observations']");
$time_layout[0] = $data->xpath("time-layout[@time-coordinate='local']");
$start_valid_time[0] = $time_layout->xpath("start-valid-time[@period-name='current']");
echo (string)$start_valid_time[0];