Drupal produces variables that can be used to enhance the functionality of themes. Typically, a function is placed in a template file. The function returns values reflecting the state of the template. A function may indicate, for example, whether the page is the front page of the site, or whether there are one, two, or three active columns. Tapping into this information is a convenient way for a theme developer to style a site dynamically.

The default Drupal variables cover the most common (and essential) functions, including creating unique identifiers for items. Some of the Drupal variables are unique to particular templates, others are common to all. In addition to the default variables, you can also define your own variables.

Let's look first at the default Drupal variables, then at intercepting and overriding the default variables, and finally, at creating your own variables.