Drupal 7 Module Development

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Chapter 3
Process functions are extremely useful when you have meta data that is likely to be
manipulated by other modules or themes and you wish to delay the rendering of the
meta data until just before the template file itself is rendered.
In the preceding code example, the template_preprocess() function creates a
$classes_array variable that holds an array of classes to be used on the wrapping
div in the template file. Modules and themes can easily add classes by simply adding
an additional array element from inside their preprocess function, as follows:
$variables['classes_array'][] = 'extra-savoir-faire';
Themes can use much simpler array manipulation functions in order to remove or
alter classes.
// Search for the bogus class and return its array key
// location. If not found, array_search returns FALSE.
// Remember that 0 is a valid key.
$key = array_search('bogus', $variables['classes_array']);
if ($key !== FALSE) {
// Alter the class.
$variables['classes_array'][$key] .= '-dude';
}
// Or remove the no-soup class.
$variables['classes_array'] = array_diff($variables['classes_array'],
array('no-soup'));
In addition to the $classes_array variable, the template_preprocess()
function also creates $attributes_array, $title_attributes_array, and
$content_attributes_array variables which are used for HTML attributes on the
outermost wrapping div, the title's heading tag, and the content's wrapping div,
respectively. You'll see each of these variables used in the typical-hook.tpl.php
example, given earlier in the chapter.
After modules and themes are given an opportunity to alter these variables, the
theme system uses the template_process() function to render those arrays into
a simple string, as follows:
function template_process(&$variables, $hook) {
// Flatten out classes.
$variables['classes'] = implode(' ', $variables['classes_array']);
// Flatten out attributes, title_attributes, and content_attributes.
$variables['attributes'] = drupal_attributes(
$variables['attributes_array']);
$variables['title_attributes'] = drupal_attributes(
$variables['title_attributes_array']);
$variables['content_attributes'] = drupal_attributes(
$variables['content_attributes_array']);
}