Method chaining allows for shorter and cleaner code, and in this article I will explain how it is possible in PHP. The best way to explain method chaining is to show you an example of it:

Without method chaining:

$abc = new Site();
$abc->add_info('title', 'Hello world!');
$abc->add_info('body', $body);
$abc->add_info('footer', 'Copyright Callum Macrae');

With method chaining:

$abc = new Site();
$abc->add_info('title', 'Hello world!')
    ->add_info('body', $body)
    ->add_info('footer', 'Copyright Callum Macrae');

Or slightly more obvious:

$abc = new Site();
$abc->add_info('title', 'Hello world!')->add_info('body', $body)->add_info('footer', 'Copyright Callum Macrae');

As you can see, the code is a lot cleaner with method chaining. Method chaining is quite commonly used in other languages, such as JavaScript. The following code excerpt is off the Node.js homepage:

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
}).listen(1337, "127.0.0.1");

Method chaining! It's clearer when displayed without the parameters:

http.createServer(function)
    .listen(port, ip);

You can do it by returning $this at the end of your methods. For example:

<?php

class EchoIt {
    private $text = array();
    public function add($text) {
        $this->text[] = $text;
        return $this;
    }

    public function out() {
        echo join($this->text, ' ') . PHP_EOL;
        $this->text = array();
        return $this;
    }
}

$text = new EchoIt;
$text->add('Hello')->add('world')->out()
    ->add('This')->add('is')->add('a')->add('test')->out();

This will output:

Hello world
This is a test

It's all fairly simple. One of the great things about this example is that PHP passes objects by reference, so the following code would do the same thing:

$text->add('Hello')->add('world');
$text->out();
$text->add('This')->add('is')->add('a')->add('test');
$text->out();