Description:
------------
According to http://www.php.net/manual/en/language.types.boolean.php it seems that in PHP 5 all objects should return TRUE when cast to boolean.  But if one creates a SimpleXML object from the string '<goodxml/>', then casts it to boolean, the result is FALSE.

As a comparison, running DOMDocument::loadxml() on "<goodxml/>" and casting the result to boolean returns TRUE.

This is important if one is doing what seems to be a quick test for failure of SimpleXML parsing, e.g. the following doesn't work as expected:

if (!simplexml_load_string($anyxml)) {
  return FALSE;  // this always executes, even for good XML
}

Reproduce code:
---------------
<?php
foreach (array('badxml', '<goodxml/>', '<goodxml>CONTENT</goodxml>') as $xml) {
  $dom = @simplexml_load_string($xml);
  print "\n\$dom from '$xml'\n";
  print '  ((boolean) $dom) = '; var_dump((boolean) $dom);
}
?>


Expected result:
----------------

$dom from 'badxml'
  ((boolean) $dom) = bool(false)

$dom from '<goodxml/>'
  ((boolean) $dom) = bool(true)

$dom from '<goodxml>CONTENT</goodxml>'
  ((boolean) $dom) = bool(true)


Actual result:
--------------

$dom from 'badxml'
  ((boolean) $dom) = bool(false)

$dom from '<goodxml/>'
  ((boolean) $dom) = bool(false)

$dom from '<goodxml>CONTENT</goodxml>'
  ((boolean) $dom) = bool(true)