Book.php

<?php 
/**
* Book Plain Old PHP class 
*/
class Book {
    
    private $title;                                                    
    private $author;                                                   
    private $current_page;
    
    // lets say it has all getter/setter method 
    public function getCurrentPage() {
        return $this->current_page;
    }

    // renders current page in plain text
    public function renderText() {
        return $this->getCurrentPage();   
    }

    // renders current page in HTML format
    public function renderHTML() {
        return "<p>{$this->getCurrentPage()}</p>";
    }
}