Calling Theme Functions
Throughout this chapter we refer to theme functions as
theme_that(). That’s what the functions are named and usually referred to as. However, you should never call a theme function directly. Doing so will reverse the wonderful functionality that comes along with Drupal’s theme layer, such as overrides, suggestions, etc. Always use the
theme() function to generate theme output. It takes care of routing the request to the appropriate theme function. For more information on how this works, see http://api.drupal.org/api/function/theme/7.