Drupal 7 Module Development

Theming a Module
}
'variables' => array(
'node' => NULL,
),
'template' => 'single-blog-block-item',
),
);
I'll explain the variables array in the very next section, but let's quickly go over the
other key now.
Since this is a theme hook, and is to be implemented using a template instead of a
theme function, we'll need to include the template key and specify the base name
of the template file, single-blog-block-item. Drupal will automatically add the
.tpl.php to the end of the base name when looking for the file, so we shouldn't
include it.
Variables versus render element
In Chapter 3, we learned about the differences between using the variables key and
using the render element key in your hook_theme(). One and only one of those keys
must be present in each theme hook declaration. However it still can be somewhat
confusing as to which to use when you are building your theme implementation.
There is only one situation in which you could use the render element key: if your
data could be represented by a single render element or by a single renderable array
containing nested render elements. If that is not the case, then you must specify the
variables key and specify the variables you will be passed to theme() and their
default values.
So does our data conform to the render element requirement above? Our $node
variable is just a partial node object and not a render element, so we must use the
variables key and specify the default values for all our variables.
As a side note, if we instead look at the way we've built the data element in the
second version of our module (a link #type render element), we can see that we
could go ahead and use render element as the key if our second version of the
module had a hook_theme() implementation.
Since the node variable is an object, we set the default value to simply be the
NULL value.
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