$row = $this->m_childlist[$i]->display ($row, $sublist); What does that mean? How to solve it

$row = $this->m_childlist[$i]->display ($row, $sublist); What does that mean?
All the code here http://bbs.csdn.net/topics/390805879

The following sentence:

function display ($row, $sublist)
{
  This is code
$row = $this->m_childlist[$i]->display ($row, $sublist);   What is the meaning of this sentence? Please advise
}

------Solution--------------------
$this->m_childlist[$i] is a TreeNode object, another 1 paragraph 46 lines:
$this->m_childlist[$count]= New TreeNode ($row [' PostID '], $row [' title '],....

$row = $this->m_childlist[$i]->display ($row, $sublist);
The function is to output all nodes and leaves along the branches.
------Solution--------------------
Look at the method should be recursive traversal tree node.

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