<?php
class Book {
  private $properties;

  function __get($property) {
    return strtolower($this->properties[$property]);
  }

  function __set($property, $value) {
    $this->properties[$property] = $value;
  }
}

$book = new Book;
$book->title = 'Code Complete';
$book->author = 'Steve McConnell';
echo $book->title . ' - ' . $book->author;