- var_dump: documentation ( source)
<?php
$subject = '<thead><tr><th>Day</th><th>Date</th><th>Duty</th><th>From</th><th>Report</th><th>To</th><th>Release</th><th>Flight Time</th><th>Duty Time</th><th>TAFB Time</th><th>Rest Time</th><th>Sector(s)/Event(s)</th></tr></thead>';
$dom = new DOMDocument();
$dom->loadHTML($subject);
$xpath = new DOMXPath($dom);
$headers = $xpath->query('//thead/tr/th');
foreach ($headers as $th) {
var_dump($th->textContent);
}