Drupal 7 Module Development

Chapter 1
The responsibility of theming a given piece of data is spread out over the Drupal
core, the modules, and the applied theme itself. While we don't modify the Drupal
core code, it is important for developers to be able to understand that both module
code and theme code can manipulate the look and feel of data.
In this book, our focus will be on the module perspective. We work primarily with
theming functions and templates that are defined within the module. Typically, it is
the best practice to work this way first—to ensure that every module has the ability
to theme it's own data.
Menus
Drupal not only maintains content, but also details about how the site itself is
organized. That is, it structures how content is related.
The principle way that it does this is through the menu subsystem. This system
provides APIs for generating, retrieving, and modifying elements that describe the
site structure. Put in common parlance, it handles the system's navigational menus.
Two menu systems?
One source of frustration for developers new to Drupal is the fact
that the application's front controller is called the menu router.
However, this system is not identical to the menu subsystem. Its
responsibility is to actually map the URLs to callback functions.
We will return to the menu router in later chapters.
Menus are hierarchical, that is, they have a tree-like structure. A menu item can have
multiple children, each of which may have their own children, and so on. In this
way, we can use the menu system to structure our site into sections and subsections.
Nodes
Perhaps the most important subsystem to know is the node system. In Drupal
parlance, a node is a piece of text-based, publishable content. It can have numerous
fields defined, but typically it has a title, a body, and various pieces of auxiliary data,
such as timestamps, publishing state, and author identification.
Nodes are content
In computer science, the term "node" often has a special meaning.
Drupal's own definition of node is distinct. It is not a point on a
graph, but rather a piece of content. One might prefer to think of
a Drupal node as a structured document.
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