A few more comments

tools/check

@@ -2,16 +2,16 @@
 #
 # Software Carpentry Lesson Validator
 #
-# Check for errors at Software Carpentry lessons.
+# Check for errors in lessons built using the Software Carpentry template
+# found at http://github.com/swcarpentry/lesson-template.
 #
 # Usage:
 #
 #     $ tools/check
 
+import sys
 import os
 import re
-import sys
-
 import yaml
 
 #----------------------------------------
@@ -62,14 +62,13 @@ def check_lesson(file_path):
     """
     Checks the file ``pages/[0-9]{2}-.*.md`` for:
 
-    - "layout: topic" at YAML header
-    - "title" as keyword at YAML header
+    - "layout: topic" in YAML header
+    - "title" as keyword in YAML header
     - line "> ## Learning Objectives {.objectives}" after YAML header
-    - items at learning objectives begin with "*"
-    - items at learning objective following four space rule
-    - code samples be of type error, output, python, shell, r, matlab, sql
+    - items in learning objectives begin with "*"
+    - items in learning objective following four-space indentation rule
+    - code samples be of type input, error, output, python, shell, r, matlab, or sql
     - callout box style
-    - line with "> ## Key Points {.keypoints}"
     - challenge box style
     """
     pass
@@ -91,11 +90,12 @@ def check_index(file_path):
 
     - "layout: lesson" in YAML header
     - "title" as keyword in YAML header
-    - introductory paragraph right after YAML header
+    - introductory paragraph(s) right after YAML header
     - line with "> ## Prerequisites"
-    - non empty prerequisites
-    - line with "## Topics"
+    - non-empty prerequisites
+    - title line with "## Topics"
     - items at topic list begin with "*"
+    - items in topic list follow four-space indentation rule
     - links at topic list are valid
     - line with "## Other Resources"
     - items at other resources list begin with "*"