Business logic versus presentation logic
We start this chapter by discussing an important architectural choice that modern applications make: how to turn data into 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 thing 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 use 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 smack in the middle of business logic but were encapsulated in a special theming function that was called by the client code. So, the separation of business logic from presentation logic...
