I just stumbled across it out of sheer desperation when I was using DOMXPath to access the text value of several single nodes:
$title = $xpath->query ('title', $ent)->item (0)->textContent;
I'm absolutely certain that when I first started (4.0? 3.x?) this was illegal since you could not follow a function call with any operator on the return value. The parser simply did not allow it and so the above code could only be written:
$nodelist = $xpath->query ('title', $ent);
$node = $nodelist->item (0);
$title = $node->textContent;
Of course, they didn't have objects then but the same was true of arrays:
$myFunction () was illegal, now it's not.