Specs: define registerElement() even more carefully: as previously defined, it didn't actually regi…

sky/specs/apis.md

 APIs
 ====
 
 The Sky core API
 ----------------
 
 ```javascript
 module 'sky:core' {
 
   // EVENTS
@@ skipping 277 matching lines @@
     // otherwise, it proceeds as follows:
     //  0. let prototype be the prototype passed in (defaulting to Element)
     //  1. let constructor be prototype.constructor
     //  2. create a new Function that:
     //      0. throws if not called as a constructor
     //      1. initialises the shadow tree is shadow on the options is true
     //      2. calls constructor, if it's not null, with the module as the argument
     //  3. let that new Function's prototype be the aforementioned prototype
     //  4. let that new Function have tagName and shadow properties set to
     //     the values passed in
+    //  5. register the new element
 
     ScriptElement? currentScript; // O(1) // returns the <script> element currently being executed if any, and if it's in this module; else null
   }
 
   class Module : AbstractModule {
     constructor (Application application, Document document, String url); // O(1)
     readonly attribute Application application; // O(1)
 
     attribute any exports; // O(1) // defaults to the module's document
   }
@@ skipping 178 matching lines @@
   the core mojo fabric JS API   sky:mojo:fabric:core
   the asyncWait/cancelWait mojo fabric JS API (interface to IPC thread)  sky:mojo:fabric:ipc
   the mojom for the shell, proxying through C++ so that the shell pipe isn't exposed  sky:mojo:shell
   the sky API  sky:core
   the sky debug symbols for private APIs  sky:debug
 ```
 
 TODO(ianh): determine if we want to separate the "this" from the
 Document, especially for Modules, so that exposing a module's element
 doesn't expose the module's exports attribute.