diff --git a/grade/report/user/lib.php b/grade/report/user/lib.php
index 7a146942e1f..ce59ea7a87a 100644
--- a/grade/report/user/lib.php
+++ b/grade/report/user/lib.php
@@ -350,6 +350,14 @@ class grade_report_user extends grade_report {
         return true;
     }
 
+    /**
+     * Fill the table with data.
+     *
+     * @param $element - An array containing the table data for the current row.
+     * @param $aggregationhints - An array that collects the aggregationhints for every
+     *                            grade_item. The hints contain grade, grademin, grademax
+     *                            status, weight and parent.
+     */
     private function fill_table_recursive(&$element, &$aggregationhints = array()) {
         global $DB, $CFG;
 
@@ -660,6 +668,8 @@ class grade_report_user extends grade_report {
             }
         }
 
+        // Check we are showing this column, and we are looking at the root of the table.
+        // This should be the very last thing this fill_table_recursive function does.
         if ($this->showcontributiontocoursetotal && ($type == 'category' && $depth == 1)) {
             // We should have collected all the hints by now - walk the tree again and build the contributions column.
 
@@ -667,6 +677,16 @@ class grade_report_user extends grade_report {
         }
     }
 
+    /**
+     * This function is called after the table has been built and the aggregationhints
+     * have been collected. We need this info to walk up the list of parents of each
+     * grade_item.
+     *
+     * @param $element - An array containing the table data for the current row.
+     * @param $aggregationhints - An array that collects the aggregationhints for every
+     *                            grade_item. The hints contain grade, grademin, grademax
+     *                            status, weight and parent.
+     */
     public function fill_contributions_column($element, $aggregationhints) {
 
         /// Recursively iterate through all child elements
@@ -675,33 +695,46 @@ class grade_report_user extends grade_report {
                 $this->fill_contributions_column($element['children'][$key], $aggregationhints);
             }
         } else if ($element['type'] == 'item') {
+            // This is a grade item (We don't do this for categories or we would double count).
             $grade_object = $element['object'];
             $itemid = $grade_object->id;
+
+            // Ignore anything with no hint - e.g. a hidden row.
             if (isset($aggregationhints[$itemid])) {
 
+                // Normalise the gradeval.
                 $graderange = $aggregationhints[$itemid]['grademax'] - $aggregationhints[$itemid]['grademin'];
                 $gradeval = ($aggregationhints[$itemid]['grade'] - $aggregationhints[$itemid]['grademin']) / $graderange;
 
+                // Multiply the normalised value by the weight
+                // of all the categories higher in the tree.
                 $parent = $aggregationhints[$itemid]['parent'];
                 do {
                     if (!is_null($aggregationhints[$itemid]['weight'])) {
                         $gradeval *= $aggregationhints[$itemid]['weight'];
                     }
 
+                    // The second part of this if is to prevent infinite loops
+                    // in case of crazy data.
                     if (isset($aggregationhints[$itemid]['parent']) &&
                         $aggregationhints[$itemid]['parent'] != $itemid) {
                         $parent = $aggregationhints[$itemid]['parent'];
                         $itemid = $parent;
                     } else {
+                        // We are at the top of the tree
                         $parent = false;
                     }
                 } while ($parent);
+                // Finally multiply by the course grademax.
                 $gradeval *= $aggregationhints[$itemid]['grademax'];
 
+                // Now we need to loop through the "built" table data and update the
+                // contributions column for the current row.
                 $header_row = "row_{$grade_object->id}_{$this->user->id}";
                 foreach ($this->tabledata as $key => $row) {
                     if (isset($row['itemname']) &&
                         ($row['itemname']['id'] == $header_row)) {
+                        // Found it - update the column.
                         $decimals = $grade_object->get_decimals();
                         $this->tabledata[$key]['contributiontocoursetotal']['content'] = format_float($gradeval, $decimals, true);
                         break;
diff --git a/lib/grade/grade_category.php b/lib/grade/grade_category.php
index 6ff24c1ccf2..d95e123cea0 100644
--- a/lib/grade/grade_category.php
+++ b/lib/grade/grade_category.php
@@ -599,6 +599,8 @@ class grade_category extends grade_object {
         unset($grade_values[$this->grade_item->id]);
 
         // Make sure a grade_grade exists for every grade_item.
+        // We need to do this so we can set the aggregationstatus
+        // with a set_field call instead of checking if each one exists and creating/updating.
         foreach ($items as $itemid => $gradeitem) {
             $gradegrade = new grade_grade(array('itemid' => $gradeitem->id,
                                                 'userid' => $userid,
@@ -630,6 +632,7 @@ class grade_category extends grade_object {
                 // If null, it means no grade.
                 if ($this->aggregateonlygraded) {
                     unset($grade_values[$itemid]);
+                    // Mark this item as dropped because it has no grade.
                     $novalue[$itemid] = 0;
                     continue;
                 }
@@ -657,6 +660,8 @@ class grade_category extends grade_object {
                 if (!$this->aggregateonlygraded) {
                     $grade_values[$itemid] = 0;
                 } else {
+                    // We are specifically marking these items that get dropped
+                    // because they are empty.
                     $novalue[$itemid] = 0;
                 }
             }
@@ -726,9 +731,11 @@ class grade_category extends grade_object {
      * @param int $userid The user we have aggregated the grades for.
      * @param array $usedweights An array with keys for each of the grade_item columns included in the aggregation. The value are the relative weight.
      * @param array $novalue An array with keys for each of the grade_item columns skipped because
-     *                       they had no value in the aggregation
+     *                       they had no value in the aggregation.
      * @param array $dropped An array with keys for each of the grade_item columns dropped
-     *                       because of any drop lowest/highest settings in the aggregation
+     *                       because of any drop lowest/highest settings in the aggregation.
+     * @param array $extracredit An array with keys for each of the grade_item columns
+     *                       considered extra credit by the aggregation.
      */
     private function set_usedinaggregation($userid, $usedweights, $novalue, $dropped, $extracredit) {
         global $DB;
diff --git a/lib/grade/grade_grade.php b/lib/grade/grade_grade.php
index b0601996247..430fbbbe704 100644
--- a/lib/grade/grade_grade.php
+++ b/lib/grade/grade_grade.php
@@ -672,6 +672,9 @@ class grade_grade extends grade_object {
      *      unknown => list of item ids that may be affected by hiding (with the calculated grade as the value)
      *      altered => list of item ids that are definitely affected by hiding (with the calculated grade as the value)
      *      alteredgrademax => for each item in altered or unknown, the new value of the grademax
+     *      alteredgrademin => for each item in altered or unknown, the new value of the grademin
+     *      alteredgradestatus => for each item with a modified status - the value of the new status
+     *      alteredgradeweight => for each item with a modified weight - the value of the new weight
      */
     public static function get_hiding_affected(&$grade_grades, &$grade_items) {
         global $CFG;