How to add a date popup calendar onto a custom form

How to use a date popup calendar within your custom module.

First, I need to download the Date module, and make my module dependent on date_popup by adding the following line into my module's .info file.

dependencies[] = date_popup

Within my form builder function:

$form['date'] = array(
'#title' => t('Arrival date'),

// Provided by the date_popup module
'#type' => 'date_popup',

// Uses the PHP date() format - http://php.net/manual/en/function.date.php
'#date_format' => 'j F Y',

// Limits the year range to the next two upcoming years
'#date_year_range' => '0:+2',

// Default value must be in 'Y-m-d' format.
'#default_value' => date('Y-m-d', time()),
);