diff --git a/tools/spec.py b/tools/spec.py
index 99e04f8..e53cd6d 100644
--- a/tools/spec.py
+++ b/tools/spec.py
@@ -903,19 +903,20 @@ if __name__ == '__main__':
 
     args = parser.parse_args()
 
-    src = open(args.src, 'r')
-
-    tree = ET.parse(src)
+    # Get a copy of the specification XML
+    with open(args.src, 'r') as src:
+        tree = ET.parse(src)
     root = tree.getroot()
 
+    # Find a parser for each of the nodes in the XML
     reg = registry()
-
-    types = {}
-
     for node in root:
         target = "parse_%s" % node.tag
         globals()[target](reg, node)
 
+    # Override some requested system types so that they fit more naturally in
+    # our environment. eg, use appropriate C++ types, or cruft library
+    # wrappers.
     reg.types['windows.h'].name = 'cruft/util/win32/windows.hpp'
     reg.types['void*'] = placeholder('void*')
     reg.types['nullptr'] = placeholder('nullptr')
@@ -924,13 +925,18 @@ if __name__ == '__main__':
     reg.types['VK_DEFINE_HANDLE'] = aliastype("VK_DEFINE_HANDLE", "void*")
     reg.types['VK_NULL_HANDLE'] = aliasvalue("VK_NULL_HANDLE", "nullptr");
 
+    # Request serialisation of all features
     features = [feature(n) for n in root.findall('./feature')]
     features = dict((f.name,f) for f in features)
 
     #reg.extensions['VK_KHR_surface'].apply(reg, platform='xcb')
+
+    # Request a minimal set of extensions that will almost certainly be
+    # required for all applications.
     extensions = ["VK_KHR_swapchain", "VK_EXT_debug_report", "VK_KHR_external_memory"]
     q = reg.serialise(args.platform)
 
+    # Finally write out the header, icd, and dispatch code.
     write_header(args.dst, q)
     write_icd(args.icd, q)
     write_dispatch(args.dispatch, q)