comments on spec and a few other things

Change-Id: I154e452946209a158a8b6fbfb7579801a8186879
diff --git a/doc/tutorial/basics/bottom.md b/doc/tutorial/basics/bottom.md
index 77be74b..8e1bf02 100644
--- a/doc/tutorial/basics/bottom.md
+++ b/doc/tutorial/basics/bottom.md
@@ -12,7 +12,7 @@
 Logically all errors are equal, although errors may be associated with
 metadata such as an error message.
 
-Note that an error is different from `null`: `null` is a valid JSON value,
+Note that an error is different from `null`: `null` is a valid value,
 whereas `_|_` is not.
 
 <!-- CUE editor -->
@@ -33,4 +33,4 @@
 l:    _|_
 list: [0, 1, 2]
 val:  _|_
-```
\ No newline at end of file
+```