Specs: Explain the parser a bit better. Make the output of registerElement() something you can pass…

sky/specs/apis.md

 APIs
 ====
 
 The Sky core API
 ----------------
 
 ```javascript
 module 'sky:core' {
 
   // EVENTS
@@ skipping 203 matching lines @@
     Object prototype = Element;
   }
 
   interface ElementConstructor {
     constructor (Dictionary attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
     constructor (ChildArguments... nodes); // shorthand
     constructor (Dictionary attributes); // shorthand
     constructor (); // shorthand
 
     constructor attribute String tagName;
+    constructor attribute Boolean shadow;
   }
 
   // MODULES
   abstract class AbstractModule : EventTarget {
     readonly attribute Document document; // O(1) // the Documentof the module or application
     Promise<any> import(String url); // O(Yikes) // returns the module's exports
 
     readonly attribute String url;
 
     // createElement() lets you create elements that will be upgraded later when you register the element
     Element createElement(String tagName, Dictionary attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
     Element createElement(String tagName, Dictionary attributes); // shorthand
     Element createElement(String tagName, ChildArguments... nodes); // shorthand
     Element createElement(String tagName); // shorthand
 
     ElementConstructor registerElement(ElementRegistration options); // O(N) in number of outstanding elements with that tag name to be upgraded
+    // if you call registerElement() with an object that was created by
+    // registerElement(), it just returns the object after registering it,
+    // rather than creating a new constructor
 
     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.