Document errors better

jedi/api/exceptions.py

@@ -3,12 +3,29 @@ class _JediError(Exception):
 
 
 class InternalError(_JediError):
-    pass
+    """
+    This error might happen a subprocess is crashing. The reason for this is
+    usually broken C code in third party libraries. This is not a very common
+    thing and it is safe to use Jedi again. However using the same calls might
+    result in the same error again.
+    """
 
 
 class WrongVersion(_JediError):
-    pass
+    """
+    This error is reserved for the future, shouldn't really be happening at the
+    moment.
+    """
 
 
 class RefactoringError(_JediError):
-    pass
+    """
+    Refactorings can fail for various reasons. So if you work with refactorings
+    like :meth:`.Script.rename`, :meth:`.Script.inline`,
+    :meth:`.Script.extract_variable` and :meth:`.Script.extract_function`, make
+    sure to catch these. The descriptions in the errors are ususally valuable
+    for end users.
+
+    A typical ``RefactoringError`` would tell the user that inlining is not
+    possible if no name is under the cursor.
+    """