I’d say recursion would be the way to go. Below is my proposal which seems to work for me. Of course, DataObjectManager’s constructor still does the shallow check so the popup size is not right but that’s another (slightly less serious) problem.

public function getNestedDOMs($fields = Null)
{
	if (!$fields) {
		$fields = $this->Fields();
	}
	
	$dom_fields = array();
	foreach ($fields as $field) {
		if ($field instanceof DataObjectManager) {
			$field->isNested = true;
			$dom_fields[] = $field;
	  	}
		
		if (method_exists($field, 'getChildren')) {
			if ($maybeFields = $this->getNestedDOMs($field->getChildren())) {
				$dom_fields[] = $maybeFields;
			}
		}
	}
	return !empty($dom_fields)? $dom_fields : false;
}

Yeah, but if there are nested tabsets, you have to recurse down. I think I'll just leave out the possibility of nested tabsets in a dom popup, though.

I like your approach.. the only thing I'd change is I'd probably evaluate "instanceof CompositeField" rather than test the getChildren() method.

As far as I can tell, this will recurse down as much as neccessary through any TabSets or other descendants of CompositeField. Am I missing something?

Whether to use instanceof or method_exists() boils down to personal taste IMO. Speaking for myself, I rather like the duck typing approach but the two options should be largely equivalent.