hooks

Via: AgileApproach Blog

Drupal Form-Handling support goes far beyond just the documented part of so-called Forms API. You can do pretty much anything with forms in Drupal and you can use/display the forms anywhere.

Here is an example. Let's assume we want to construct a custom node type with custom fields, using CCK. Then we want to display this form into some non-standard page. To further complicate things, let's assume we also want custom verification and processing routines.

And last but not least - we want to use full power of Drupal and write a minimal amount of code. Following is a snippet demonstrating key points to achieving this task (thorough understanding of Drupal is required):