diff --git a/lib/accesslib.php b/lib/accesslib.php
index 447535704a5..f50c23fa71a 100644
--- a/lib/accesslib.php
+++ b/lib/accesslib.php
@@ -6222,7 +6222,7 @@ class context_system extends context {
      * Returns system context instance.
      *
      * @static
-     * @param int $instanceid
+     * @param int $instanceid should be 0
      * @param int $strictness
      * @param bool $cache
      * @return context_system context instance
@@ -6474,19 +6474,19 @@ class context_user extends context {
      * Returns user context instance.
      *
      * @static
-     * @param int $instanceid
+     * @param int $userid id from {user} table
      * @param int $strictness
      * @return context_user context instance
      */
-    public static function instance($instanceid, $strictness = MUST_EXIST) {
+    public static function instance($userid, $strictness = MUST_EXIST) {
         global $DB;
 
-        if ($context = context::cache_get(CONTEXT_USER, $instanceid)) {
+        if ($context = context::cache_get(CONTEXT_USER, $userid)) {
             return $context;
         }
 
-        if (!$record = $DB->get_record('context', array('contextlevel'=>CONTEXT_USER, 'instanceid'=>$instanceid))) {
-            if ($user = $DB->get_record('user', array('id'=>$instanceid, 'deleted'=>0), 'id', $strictness)) {
+        if (!$record = $DB->get_record('context', array('contextlevel' => CONTEXT_USER, 'instanceid' => $userid))) {
+            if ($user = $DB->get_record('user', array('id' => $userid, 'deleted' => 0), 'id', $strictness)) {
                 $record = context::insert_context_record(CONTEXT_USER, $user->id, '/'.SYSCONTEXTID, 0);
             }
         }
@@ -6652,19 +6652,19 @@ class context_coursecat extends context {
      * Returns course category context instance.
      *
      * @static
-     * @param int $instanceid
+     * @param int $categoryid id from {course_categories} table
      * @param int $strictness
      * @return context_coursecat context instance
      */
-    public static function instance($instanceid, $strictness = MUST_EXIST) {
+    public static function instance($categoryid, $strictness = MUST_EXIST) {
         global $DB;
 
-        if ($context = context::cache_get(CONTEXT_COURSECAT, $instanceid)) {
+        if ($context = context::cache_get(CONTEXT_COURSECAT, $categoryid)) {
             return $context;
         }
 
-        if (!$record = $DB->get_record('context', array('contextlevel'=>CONTEXT_COURSECAT, 'instanceid'=>$instanceid))) {
-            if ($category = $DB->get_record('course_categories', array('id'=>$instanceid), 'id,parent', $strictness)) {
+        if (!$record = $DB->get_record('context', array('contextlevel' => CONTEXT_COURSECAT, 'instanceid' => $categoryid))) {
+            if ($category = $DB->get_record('course_categories', array('id' => $categoryid), 'id,parent', $strictness)) {
                 if ($category->parent) {
                     $parentcontext = context_coursecat::instance($category->parent);
                     $record = context::insert_context_record(CONTEXT_COURSECAT, $category->id, $parentcontext->path);
@@ -6906,19 +6906,19 @@ class context_course extends context {
      * Returns course context instance.
      *
      * @static
-     * @param int $instanceid
+     * @param int $courseid id from {course} table
      * @param int $strictness
      * @return context_course context instance
      */
-    public static function instance($instanceid, $strictness = MUST_EXIST) {
+    public static function instance($courseid, $strictness = MUST_EXIST) {
         global $DB;
 
-        if ($context = context::cache_get(CONTEXT_COURSE, $instanceid)) {
+        if ($context = context::cache_get(CONTEXT_COURSE, $courseid)) {
             return $context;
         }
 
-        if (!$record = $DB->get_record('context', array('contextlevel'=>CONTEXT_COURSE, 'instanceid'=>$instanceid))) {
-            if ($course = $DB->get_record('course', array('id'=>$instanceid), 'id,category', $strictness)) {
+        if (!$record = $DB->get_record('context', array('contextlevel' => CONTEXT_COURSE, 'instanceid' => $courseid))) {
+            if ($course = $DB->get_record('course', array('id' => $courseid), 'id,category', $strictness)) {
                 if ($course->category) {
                     $parentcontext = context_coursecat::instance($course->category);
                     $record = context::insert_context_record(CONTEXT_COURSE, $course->id, $parentcontext->path);
@@ -7167,19 +7167,19 @@ class context_module extends context {
      * Returns module context instance.
      *
      * @static
-     * @param int $instanceid
+     * @param int $cmid id of the record from {course_modules} table; pass cmid there, NOT id in the instance column
      * @param int $strictness
      * @return context_module context instance
      */
-    public static function instance($instanceid, $strictness = MUST_EXIST) {
+    public static function instance($cmid, $strictness = MUST_EXIST) {
         global $DB;
 
-        if ($context = context::cache_get(CONTEXT_MODULE, $instanceid)) {
+        if ($context = context::cache_get(CONTEXT_MODULE, $cmid)) {
             return $context;
         }
 
-        if (!$record = $DB->get_record('context', array('contextlevel'=>CONTEXT_MODULE, 'instanceid'=>$instanceid))) {
-            if ($cm = $DB->get_record('course_modules', array('id'=>$instanceid), 'id,course', $strictness)) {
+        if (!$record = $DB->get_record('context', array('contextlevel' => CONTEXT_MODULE, 'instanceid' => $cmid))) {
+            if ($cm = $DB->get_record('course_modules', array('id' => $cmid), 'id,course', $strictness)) {
                 $parentcontext = context_course::instance($cm->course);
                 $record = context::insert_context_record(CONTEXT_MODULE, $cm->id, $parentcontext->path);
             }
@@ -7379,19 +7379,19 @@ class context_block extends context {
      * Returns block context instance.
      *
      * @static
-     * @param int $instanceid
+     * @param int $blockinstanceid id from {block_instances} table.
      * @param int $strictness
      * @return context_block context instance
      */
-    public static function instance($instanceid, $strictness = MUST_EXIST) {
+    public static function instance($blockinstanceid, $strictness = MUST_EXIST) {
         global $DB;
 
-        if ($context = context::cache_get(CONTEXT_BLOCK, $instanceid)) {
+        if ($context = context::cache_get(CONTEXT_BLOCK, $blockinstanceid)) {
             return $context;
         }
 
-        if (!$record = $DB->get_record('context', array('contextlevel'=>CONTEXT_BLOCK, 'instanceid'=>$instanceid))) {
-            if ($bi = $DB->get_record('block_instances', array('id'=>$instanceid), 'id,parentcontextid', $strictness)) {
+        if (!$record = $DB->get_record('context', array('contextlevel' => CONTEXT_BLOCK, 'instanceid' => $blockinstanceid))) {
+            if ($bi = $DB->get_record('block_instances', array('id' => $blockinstanceid), 'id,parentcontextid', $strictness)) {
                 $parentcontext = context::instance_by_id($bi->parentcontextid);
                 $record = context::insert_context_record(CONTEXT_BLOCK, $bi->id, $parentcontext->path);
             }