Forum posts in php can be expanded, so the book knowledge cannot be understood ~ Please help me

Forum posts in php are displayed, and the book knowledge cannot be understood ~, Please help me, & lt ;? Php & nbsp; functions & nbsp; for & nbsp; loading, & nbsp; contructing & nbsp; and & nbsp; displaying & nbsp; the & nbsp; tree & nbsp; are & nbsp; in & nbsp; this & nbsp; f forum posts in php. you can't understand the book knowledge ~, Please help me,

 // functions for loading, contructing and 
// displaying the tree are in this file 

class treenode
{ 
  // each node in the tree has member variables containing 
  // all the data for a post except the body of the message
  public $m_postid;
  public $m_title;
  public $m_poster;
  public $m_posted;
  public $m_children;
  public $m_childlist;
  public $m_depth;

  public function __construct($postid, $title, $poster, $posted, $children, 
                    $expand, $depth, $expanded, $sublist)
  { 
    // the constructor sets up the member variables, but more 
    // importantly recursively creates lower parts of the tree
    $this->m_postid = $postid;
    $this->m_title = $title;
    $this->m_poster = $poster;
    $this->m_posted = $posted;
    $this->m_children =$children;
    $this->m_childlist = array();
    $this->m_depth = $depth;

    // we only care what is below this node if it 
    // has children and is marked to be expanded
    // sublists are always expanded
    if(($sublist||$expand) && $children)
    {
      $conn = db_connect();

      $query = "select * from header where parent = $postid order by posted";
      $result = $conn->query($query);

      for ($count=0; $row = @$result->fetch_assoc(); $count++)
      {
        if($sublist||$expanded[ $row['postid'] ] == true)
          $expand = true;
        else
          $expand = false;
        $this->m_childlist[$count]= new treenode($row['postid'],$row['title'],
                                      $row['poster'],$row['posted'],
                                      $row['children'], $expand,
                                      $depth+1, $expanded, $sublist);
      }
    }
  }  


  function display($row, $sublist = false)
  {
    // as this is an object, it is responsible for displaying itself

    // $row tells us what row of the display we are up to 
    // so we know what color it should be

    // $sublist tells us whether we are on the main page
    // or the message page.  Message pages should have 
    // $sublist = true.  
    // On a sublist, all messages are expanded and there are
    // no "+" or "-" symbols.

    // if this is the empty root node skip displaying
    if($this->m_depth>-1)  
    {
      //color alternate rows
      echo '";
      else
        echo "'#ffffff'>";

      // indent replies to the depth of nesting