Specs: fix a raft of syntax errors caught by actually running a syntax checker...

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:
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   final String url;
 
   final Root elements; // O(1)
   // the Root node of the module or application's element tree
 
   external Future<Module> import(String url); // O(Yikes)
   // load and return the URL at the given Module
   // if it's already loaded, the future will resolve immediately
   // if loading fails, the future will have an error
 
-  List<Module> getImports(); // O(N)
+  external List<Module> getImports(); // O(N)
   // returns the Module objects of all the imported modules
 
   external void registerElement(String tagname, Type elementClass); // O(1)
   // registers a tag name with the parser
   // only useful during parse time
   // verify that tagname isn't null or empty
   // verify that elementClass is the Type of a class that extends Element (directly or indirectly, but not via "implements" or "with")
   // (see the @tagname code for an example of how to verify that from dart)
   // verify that there's not already a class registered for this tag name
   // if there is, then mark this tagname is broken, so that it acts as if it's not registered in the parser,
   // and, if this is the first time it was marked broken, log a console message regarding the issue
   // (mention the tag name but not the classes, so that it's not observable that this currently happens out of order)
 }
 
 class Module extends AbstractModule {
   Module({String url, Root elements, this.application}) :
     super(url: url, elements: elements); // O(1)
   final Application application; // O(1)
 }
 
 class Application extends AbstractModule {
   Application({String url, Root elements, this.gestureManager}) :
     super(url: url, elements: elements); // O(1)
   external String get title; // O(1)
   external void set title(String newValue); // O(1)
   final GestureManager gestureManager;
 }
 ```