Update to include two separate metadata callbacks as opposed to one.

includes/metadata.inc

@@ -16,13 +16,39 @@
 function islandora_retrieve_metadata_markup(AbstractObject $object) {
   $viewers = module_invoke_all('islandora_metadata_display_info');
   $viewer = variable_get('islandora_metadata_display', 'dublin_core');
+  $markup = '';
+  if (isset($viewers[$viewer]['metadata callback'])) {
+    $markup = call_user_func($viewers[$viewer]['metadata callback'], $object);
+    // The callback doesn't have any markup provided for this particular object,
+    // default back to the dublin_core display.
+    if ($markup === FALSE) {
+      $markup = call_user_func($viewers['dublin_core']['metadata callback'], $object);
+    }
+  }
+  return $markup;
+}
 
-  if (isset($viewers[$viewer]['callback'])) {
-    return call_user_func($viewers[$viewer]['callback'], $object);
+/**
+ * Retrieves the metadata display description for an Islandora object.
+ *
+ * @param AbstractObject $object
+ *   An AbstractObject representing an object within Fedora.
+ * @return string
+ *   Markup to be rendered for description on Islandora object pages.
+ */
+function islandora_retrieve_description_markup(AbstractObject $object) {
+  $viewers = module_invoke_all('islandora_metadata_display_info');
+  $viewer = variable_get('islandora_metadata_display', 'dublin_core');
+  $markup = '';
+  if (isset($viewers[$viewer]['description callback'])) {
+    $markup = call_user_func($viewers[$viewer]['description callback'], $object);
+    // The callback doesn't have any markup provided for this particular object,
+    // default back to the dublin_core display.
+    if ($markup === FALSE) {
+      $markup = call_user_func($viewers['dublin_core']['description callback'], $object);
     }
-  else {
-    return '';
   }
+  return $markup;
 }
 
 /**
@@ -121,3 +147,30 @@ function islandora_metadata_display_callback(AbstractObject $object) {
   );
   return theme('islandora_dublin_core_display', $elements);
 }
+
+/**
+ * Metadata description callback for rendering Dublin Core description.
+ *
+ * @param AbstractObject $object
+ *   An AbstractObject representing an object within Fedora.
+ *
+ * @return string
+ *   Markup representing the rendered metadata from Dublin Core.
+ */
+function islandora_metadata_description_callback(AbstractObject $islandora_object) {
+  if (islandora_datastream_access(ISLANDORA_VIEW_OBJECTS, $islandora_object['DC'])) {
+    try {
+      $dc = $islandora_object['DC']->content;
+      $dc_object = DublinCore::importFromXMLString($dc);
+    }
+    catch (Exception $e) {
+      drupal_set_message(t('Error retrieving object %s %t', array('%s' => $islandora_object->id, '%t' => $e->getMessage())), 'error', FALSE);
+    }
+  }
+  $dc_array = isset($dc_object) ? $dc_object->asArray() : array();
+  $elements = array(
+    'islandora_object' => $islandora_object,
+    'dc_array' => $dc_array,
+  );
+  return theme('islandora_dublin_core_description', $elements);
+}

islandora.api.php

@@ -714,7 +714,8 @@ function hook_islandora_metadata_display_info() {
     'hookable_displays_yay' => array(
       'label' => t('Hookable display yay!'),
       'description' => t('This is purely an example of how to implement this.'),
-      'callback' => 'hookable_displays_some_function_that_returns_markup',
+      'metadata callback' => 'hookable_displays_some_function_that_returns_metadata_markup',
+      'description callback' => 'hookable_displays_some_function_that_returns_description_markup',
       'configuration' => 'admin/hookable_displays_yay/somepath',
     ),
   );

islandora.module

@@ -464,6 +464,17 @@ function islandora_theme() {
       'pattern' => 'islandora_dublin_core_display__',
       'variables' => array('islandora_object' => NULL),
     ),
+    'islandora_dublin_core_description' => array(
+      'file' => 'theme/theme.inc',
+      'template' => 'theme/islandora-dublin-core-description',
+      // We can add PIDs to the end of this pattern in our preprocess function
+      // and templates will be able to have have a pid appended to the
+      // template name to overide a template on a per object basis.
+      // An example template might be named:
+      // "islandora-dublin-core-description--islandora-27.tpl.php".
+      'pattern' => 'islandora_dublin_core_description__',
+      'variables' => array('islandora_object' => NULL),
+    ),
   );
 }
 
@@ -1630,7 +1641,8 @@ function islandora_islandora_metadata_display_info() {
     'dublin_core' => array(
       'label' => t('Dublin Core'),
       'description' => t('Dublin Core metadata'),
-      'callback' => 'islandora_metadata_display_callback',
+      'metadata callback' => 'islandora_metadata_display_callback',
+      'description callback' => 'islandora_metadata_description_callback',
     ),
   );
 }

theme/islandora-dublin-core-description.tpl.php

@@ -0,0 +1,20 @@
+<?php
+/**
+ * @file
+ * This is the template file for the Dublin Core metadata description.
+ *
+ * Available variables:
+ * - $islandora_object: The Islandora object rendered in this template file
+ * $dc_array: The DC datastream object values as a sanitized array. This
+ * includes label, value and class name.
+ *
+ * @see template_preprocess_islandora_dublin_core_description()
+ * @see theme_islandora_dublin_core_description()
+ */
+?>
+<div class="islandora-metadata-sidebar">
+  <?php if (!empty($dc_array['dc:description']['value'])): ?>
+    <h2><?php print $dc_array['dc:description']['label']; ?></h2>
+    <p property="description"><?php print $dc_array['dc:description']['value']; ?></p>
+  <?php endif; ?>
+</div>

theme/islandora-dublin-core-display.tpl.php

@@ -1,3 +1,21 @@
+<?php
+/**
+* @file
+* This is the template file for the object page for large image
+*
+* Available variables:
+* - $islandora_object: The Islandora object rendered in this template file
+* - $islandora_dublin_core: The DC datastream object
+* - $dc_array: The DC datastream object values as a sanitized array. This
+* includes label, value and class name.
+* - $islandora_object_label: The sanitized object label.
+* - $parent_collections: An array containing parent collection(s) info.
+* Includes collection object, label, url and rendered link.
+*
+* @see template_preprocess_islandora_dublin_core_display()
+* @see theme_islandora_dublin_core_display()
+*/
+?>
 <fieldset class="collapsible collapsed">
   <legend><span class="fieldset-legend"><?php print t('Details'); ?></span></legend>
   <div class="fieldset-wrapper">

theme/theme.inc

@@ -438,6 +438,22 @@ function islandora_preprocess_islandora_dublin_core_display(array &$variables) {
       drupal_set_message(t('Error retrieving object %s %t', array('%s' => $islandora_object->id, '%t' => $e->getMessage())), 'error', FALSE);
     }
   }
-  $variables['islandora_dublin_core'] = isset($dc_object) ? $dc_object : NULL;
+  $variables['dc_array'] = isset($dc_object) ? $dc_object->asArray() : array();
+}
+
+/**
+ * Implements hook_preprocess().
+ */
+function islandora_preprocess_islandora_dublin_core_description(array &$variables) {
+  $islandora_object = $variables['islandora_object'];
+  if (islandora_datastream_access(ISLANDORA_VIEW_OBJECTS, $islandora_object['DC'])) {
+    try {
+      $dc = $islandora_object['DC']->content;
+      $dc_object = DublinCore::importFromXMLString($dc);
+    }
+    catch (Exception $e) {
+      drupal_set_message(t('Error retrieving object %s %t', array('%s' => $islandora_object->id, '%t' => $e->getMessage())), 'error', FALSE);
+    }
+  }
   $variables['dc_array'] = isset($dc_object) ? $dc_object->asArray() : array();
 }