added docs and added is_correct to conditional

common/lib/xmodule/xmodule/capa_module.py

@@ -517,8 +517,14 @@ class CapaModule(CapaFields, XModule):
         return False
 
     def is_completed(self):
-        # used by conditional module
-        # return self.answer_available()
+        """ Used to decide to show or hide RESET or CHECK buttons.
+
+        Actually means that student submitted problem and nothing more.
+        Problem can be completely wrong.
+        Pressing RESET button makes this function to return False.
+        Suggestion: rename it to is_submitted.
+
+        # older comment: return self.answer_available()"""
         return self.lcp.done
 
     def is_attempted(self):

common/lib/xmodule/xmodule/conditional_module.py

@@ -70,8 +70,18 @@ class ConditionalModule(ConditionalFields, XModule):
     # value: <name of module attribute>
     conditions_map = {
         'poll_answer': 'poll_answer',  # poll_question attr
+
+        # problem was submitted (it can be wrong)
+        # if student will press reset button after that,
+        # state will be reverted
         'completed': 'is_completed',  # capa_problem attr
+
+        # if student attempted problem
         'attempted': 'is_attempted',  # capa_problem attr
+
+        # if problem is full points
+        'correct': 'is_correct',
+
         'voted': 'voted'  # poll_question attr
     }