More documentation!

elements/core/doc.go

@@ -2,6 +2,6 @@
 // interfaces without having to duplicate a ton of code. Each "core" is a type
 // that can be embedded into an element directly, working to fulfill a
 // particular interface. Each one comes with a corresponding core control, which
-// provides an interface for elements to exert control over the core. They
-// should be kept private.
+// provides an interface for elements to exert control over the core. Core
+// controls should be kept private.
 package core