For the sake of completeness, here is the full list of all the classes developed during the series. I hope you enjoy studying them and introducing your own modifications. See you soon!

// interface HTMLRenderer
// defines generic method toHTML()
interface HTMLRenderer {
    public abstract function toHTML();
}
// class MySQL
class MySQL{
    private $conId; // connection identifier
    private $host; // MySQL host
    private $user; // MySQL username
    private $password; // MySQL password
    private $database; // MySQL database
    // constructor
    public function __construct($options=array()){
        // validate incoming parameters
        if(count($options)<4){
            throw new Exception('Invalid number of connection
parameters');
        }
        foreach($options as $parameter=>$value){
            if(!$parameter||!$value){
                throw new Exception('Invalid connection
parameters');
            }
            $this->{$parameter}=$value;
        }
        // connect to MySQL
 $this->connectDB();
        }
        // connect to MYSQL server and select database
        private function connectDB(){
            if(!$this->conId=mysql_connect($this->host,$this-
>user,$this->password)){
                 throw new Exception('Error connecting to the server');
 }
 if(!mysql_select_db($this->database,$this->conId)){
     throw new Exception('Error selecting database');
 }
        }
        // perform query
        public function query($query){
 if(!$this->result=mysql_query($query,$this->conId)){
     throw new Exception('Error performing query '.$query);
 }
 // return new Result object
 return new Result($this,$this->result);
       }
}
//class Result
class Result implements HTMLRenderer{
    private $output; // dynamic output
    private $mysql; // instance of MySQL object
    private $result; // MySQL result set
    // constructor
    public function __construct($mysql,$result){
        $this->mysql=$mysql;
        $this->result=$result;
    }
    // fetch row
    public function fetchRow(){
        return mysql_fetch_array($this->result,MYSQL_ASSOC);
    }
    // count rows
    public function countRows(){
        if(!$rows=mysql_num_rows($this->result)){
            throw new Exception('Error counting rows');
        }
        return $rows;
    }
    // count affected rows
    public function countAffectedRows(){
        if(!$rows=mysql_affected_rows($this->mysql->conId)){
 throw new Exception('Error counting affected rows');
        }
        return $rows;
    }
    // get ID from last inserted row
    public function getInsertID(){
        if(!$id=mysql_insert_id($this->mysql->conId)){
 throw new Exception('Error getting ID');
        }
        return $id;
    }
    // seek row
    public function seekRow($row=0){
        if(!mysql_data_seek($this->result,$row)){
 throw new Exception('Error seeking data');
        }
    }
    // return HTML rendered result set
    public function toHTML(){
        $this->output='<table>';
        while($row=$this->fetchRow()){
            $this->output.='<tr>';
            foreach($row as $field=>$value){
                $this->output.='<td>'.$value.'</td>';
            }
            $this->output.='</tr>';
        }
        $this->output.='</table>';
        return $this->output;
    }
}
// ************************************
// begin of core class definitions
// ************************************
// class ObjectFactory - returns HTML widget objects
abstract class ObjectFactory{
    private function __construct(){}
    public function createObject($type,$attributes=array()){
        if(!class_exists($type)||!is_array($attributes)){
            throw new Exception('Invalid object parameters');
        }
        return new $type($attributes);
    }
}
// class PageGenerator - creates web pages
class PageGenerator{
    private $output;
    private $title;
    private $keywords;
    private $cssFile;
    private $jsFile;
    public function __construct(){
        $this->output='';
        $this->title='Sample Page';
        $this->keywords='PHP,Interfaces,OOP,Type,Hinting';
        $this->cssFile='styles.css';
        $this->jsFile='global_functions.js';
    }
    public function setTitle($title){
        $this->title=$title;
    }
    public function setKeywords($keywords){
        $this->keywords=$keywords;
    }
    public function setCssFile($cssFile){
        $this->cssFile=$cssFile;
    }
    public function setJsFile($jsFile){
        $this->jsFile=$jsFile;
    }
    public function makeHeader(){
        $this->output='<html><head><title>'.$this-
>title.'</title><meta name="keywords" content="'.$this-
>keywords.'" /><link rel="stylesheet" href="'.$this->cssFile.'"
type="text/css"><script language="javascript" src="'.$this-
>jsFile.'"></script></head><body>';
    }
    public function addHTMLRenderableObject(HTMLRenderer $object){
        $this->output.=$object->toHTML();
    }
    public function makeFooter(){
        $this->output.='</body></html>';
    }
    public function getHTML(){
        return $this->output;
    }
}
// *********************************************
// end of core class definitions
// *********************************************
// *********************************************
// begin of HTML widget class definitions
// *********************************************
// class Table
class Table implements HTMLRenderer{
    private $output='<table ';
    private $data=array();
    private $attributes=array();
    public function __construct($attributes=array()){
        if(count($attributes)<1){
            throw new Exception('Invalid number of attributes');
        }
        $this->attributes=$attributes;
    }
    public function setData($data=array()){
        if(count($data)<1){
            throw new Exception('Empty data set');
        }
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        foreach($this->data as $data){
            $data=($data instanceof HTMLRenderer)?$data->toHTML
():$data;
            $this->output.='<tr><td>'.$data.'</td></tr>';
        }
        $this->output.='</table>';
        return $this->output;
    }
}
// class Div
class Div implements HTMLRenderer{
    private $output='<div ';
    private $data;
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data){
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?
$this->data->toHTML():$this->data;
        $this->output.='</div>';
        return $this->output;
    }
}
// class Header1
class Header1 implements HTMLRenderer{
    private $output='<h1 ';
    private $data;
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data){
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?
$this->data->toHTML():$this->data;
        $this->output.='</h1>';
        return $this->output;
    }
}
// class Header2
class Header2 implements HTMLRenderer{
    private $output='<h2 ';
    private $data;
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data){
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?
$this->data->toHTML():$this->data;
        $this->output.='</h2>';
        return $this->output;
    }
}
// class Header3
class Header3 implements HTMLRenderer{
    private $output='<h3 ';
    private $data;
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data){
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?
$this->data->toHTML():$this->data;
        $this->output.='</h3>';
        return $this->output;
    }
}
// class Header4
class Header4 implements HTMLRenderer{
    private $output='<h4 ';
    private $data;
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data){
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?
$this->data->toHTML():$this->data;
        $this->output.='</h4>';
        return $this->output;
    }
}
// class Header5
class Header5 implements HTMLRenderer{
    private $output='<h5 ';
    private $data;
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data){
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?
$this->data->toHTML():$this->data;
        $this->output.='</h5>';
        return $this->output;
    }
}
// class Header6
class Header6 implements HTMLRenderer{
    private $output='<h6 ';
    private $data;
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data){
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?
$this->data->toHTML():$this->data;
        $this->output.='</h6>';
        return $this->output;
    }
}
// class Paragraph
class Paragraph implements HTMLRenderer{
    private $output='<p ';
    private $data;
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data){
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?
$this->data->toHTML():$this->data;
        $this->output.='</p>';
        return $this->output;
    }
}
// class HTMLlist
class HTMLlist implements HTMLRenderer{
    private $output='<ul ';
    private $data=array();
    private $attributes=array();
    public function __construct($attributes=array()){
        $this->attributes=$attributes;
    }
    public function setData($data=array()){
        if(count($data)<1){
            throw new Exception('Empty data set');
        }
        $this->data=$data;
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        foreach($this->data as $data){
            $data=($data instanceof HTMLRenderer)?$data->toHTML
():$data;
            $this->output.='<li>'.$data.'</li>';
        }
        $this->output.='</ul>';
        return $this->output;
    }
}
// class Form
class Form implements HTMLRenderer{
    private $output='<form ';
    private $data;
    private $fields=array();
    private $attributes=array();
    public function __construct($attributes){
        $this->attributes=$attributes;
    }
    // set generic form data
    public function setData($data){
        $this->data=$data;
    }
    // add <input> element
    public function addInputField($fieldAttributes=array
(),$inputPart=''){
        $fieldOutput=$inputPart.'<input ';
        foreach($fieldAttributes as $attribute=>$value){
            $fieldOutput.=$attribute.'="'.$value.'" ';
        }
        $this->fields[]=$fieldOutput.'/>';
    }
    // add <textarea> element
    public function addTextArea($fieldAttributes=array
(),$inputPart=''){
        $fieldOutput=$inputPart.'<textarea ';
        foreach($fieldAttributes as $attribute=>$value){
            $fieldOutput.=$attribute.'="'.$value.'" ';
        }
        $fieldOutput=substr_replace($fieldOutput,'>',-1);
        $this->fields[]=$fieldOutput.'</textarea>';
    }
    // add <select> element
    public function addSelectField($fieldAttributes=array(),$options=array(),$inputPart=''){
        $fieldOutput=$inputPart.'<select ';
        foreach($fieldAttributes as $attribute=>$value){
            $fieldOutput.=$attribute.'="'.$value.'" ';
        }
        $fieldOutput=substr_replace($fieldOutput,'>',-1);
        foreach($options as $option=>$value){
            $fieldOutput.='<option
value="'.$value.'">'.$option.'</option>';
        }
        $this->fields[]=$fieldOutput.'</select>';
       
    }
    public function toHTML(){
        foreach($this->attributes as $attribute=>$value){
            $this->output.=$attribute.'="'.$value.'" ';
        }
        $this->output=substr_replace($this->output,'>',-1);
        $this->output.=($this->data instanceof HTMLRenderer)?$this->data->toHTML():$this->data;
        foreach($this->fields as $field){
            $this->output.=$field;
        }
        $this->output.='</form>';
        return $this->output;
    }
}
// *******************************************
// end of HTML widget class definitions
// *******************************************

Note: all the classes have been tested on Apache 2.0.48 and PHP 5.0.4.