Theme engine integration
Your site's theme may have special content and features that do not exist in Drupal themes. This section will explain how you can use your own themes using Drupal's theme engines. If all you need to achieve a common "look and feel", you do not need to modify a theme engine, you can simply create a new template based on your site's design elements.
Drupal currently has the following theme engines: Xtemplate, PHPTemplate, Smarty and Plain PHP. You can read an in-depth explanation of these template engines in the Theme developer's guide.
Of these four theme engines, the simplest for integration purposes is the Plain PHP method.
In most cases, your theme integration will require a header and a footer. Those two regions will require elements from both Drupal and your application, particularly to include Java scripts used by both applications and onload elements.
Having read the Plain PHP guide, the integration with your templates will simply require including your application's template engine (if not already included elsewhere, like in settings.php), and adding any required globals from within your plain PHP theme.
Example:
"Example to follow after checking why PHP snippets cannot be added here.."
