Drupal is a comprehensive framework for managing website content. It can be used to create, publish and edit websites with a few simple clicks using the standard theme functionalities of the Drupal interface. The basic theme functionalities of Drupal such as the box, nodes, comments, block, and pages are set by default in the system. It can be used for any type of designing task and can be very handy for users without deep knowledge of PHP programming.
For advanced users who want to customize the site functions, the default Drupal template PHP theme can be overridden by editing the theme source codes. Drupal is created using the PHP language so users need to learn basic PHP programming in order to override the default Drupal template functions.
To perform the operation, users need to create a specific template PHP file on the Drupal theme directory. By referring to the API documentation, users can find the list of themes and functions that can be overridden using the template PHP file.
Administrators then can write the PHP codes that will create new functionalities and themes for the Drupal site. The standard themes can be rewritten or some functions can be trimmed down. This operation involves lots of coding in PHP so it would be suitable for those who have enough background on this type of programming language.
Aside from editing or overriding some or all of the themes and functionalities in the Drupal framework, administrators of the site can also change the default forms available on it.