We will start this chapter by discussing an important architectural choice modern applications make--how to turn data into a presentation.
So, what would be the best way to get our data and functionality marked up? Do we simply wrap each piece of data in HTML and return the whole as a giant string, as shown in the following example?
return '<div class="wrapper">' . $data . '</div>';
No, we don't. Like all other well-designed applications, Drupal separates its business logic from its presentation logic. It's true, previous versions of Drupal did have this kind of approach, especially when it came to theme functions, but even so, they were easily overridable. So, constructs like these were not found ...