Specs: Drop the concept of late-bound elements. An element can never be upgraded.

sky/specs/modules.md

 Sky Module System
 =================
 
 This document describes the Sky module system.
 
 Overview
 --------
 
 The Sky module system is based on the ```import``` element. In its
 most basic form, you import a module as follows:
 
 ```html
 <import src="path/to/module.sky" />
 ```
 
 As these ```import``` elements are inserted into a document, the
 document's list of outstanding dependencies grows. When an imported
 module completes, it is removed from the document's list of
 outstanding dependencies.
 
-Before executing any ```script``` elements, the parser waits until the
-list of outstanding dependencies is empty. After the parser has
-finished parsing, the document waits until its list of outstanding
-dependencies is empty before the module it represents is marked
-complete.
+Before executing script or inserting an element that is not already
+registered, the parser waits until the list of outstanding
+dependencies is empty. After the parser has finished parsing, the
+document waits until its list of outstanding dependencies is empty
+before the module it represents is marked complete.
 
 
 Module API
 ----------
 
 Within a script in a module, the ```module``` identifier is bound to
-the ```Module``` object that represents the module:
-
-```javascript
-interface Module : EventTarget {
-  constructor (Application application, Document document); // O(1)
-  attribute any exports; // O(1) // defaults to the module's document
-  readonly attribute Document document; // O(1) // the module's document
-  readonly attribute Application application; // O(1)
-}
-```
+the [```Module``` object](apis.md) that represents the module.
 
 ### Exporting values ###
 
 A module can export a value by assigning the ```exports``` property of
 its ```Module``` object. By default, the ```exports``` property of a
 ```Module``` is its ```Document``` object, so that a script-less
 import is still useful (it exposes its contents, e.g. templates that
 the import might have been written to provide).
 
 ### Exporting element definitions ###
@@ skipping 25 matching lines @@
 Where ```name_1``` through ```name_n``` are the names bound to the
 various named imports in the script element's document,
 ```source_code``` is the text content of the script element,
 ```source_module`` is the ```Module``` object of the script element's
 module, and ```value_1``` through ```value_n``` are the values
 exported by the various named imports in the script element's
 document.
 
 When an import fails to load, the ```as``` name for the import gets
 bound to ```undefined```.