<?php
$source = '
<body class="foobar"></body>
<body data-foobar="foo>bar"> foobar"></body>
';
$bodyTag = "foobar";
'/<body([\S\s][^>]*)>/',
'<body$1><noscript>' . $bodyTag . '</noscript>',
$source
);
echo $source;
PD9waHAKIAokc291cmNlID0gJwo8Ym9keSBjbGFzcz0iZm9vYmFyIj48L2JvZHk+Cjxib2R5IGRhdGEtZm9vYmFyPSJmb28+YmFyIj4gZm9vYmFyIj48L2JvZHk+Cic7CiAKJGJvZHlUYWcgPSAiZm9vYmFyIjsKIAokc291cmNlID0gcHJlZ19yZXBsYWNlKAogICAgJy88Ym9keShbXFNcc11bXj5dKik+LycsCiAgICAnPGJvZHkkMT48bm9zY3JpcHQ+JyAuICRib2R5VGFnIC4gJzwvbm9zY3JpcHQ+JywKICAgICRzb3VyY2UKKTsKIAplY2hvICRzb3VyY2U7