title: typescript multi-file namespaces export error
body: <p>"You can split a namespace across many files. Even though the files are separate, they can each contribute to the same namespace and can be consumed as if they were all defined in one place. Because there are dependencies between files, you will add reference tags to tell the compiler about the relationships between the files."</p>
  
  <pre><code>//ZooAnimals.ts
  
  namespace Zoo { 
      interface Animal { 
           skinType: string;
          isMammal(): boolean;
      }
  }
  
  //ZooWild.ts
  
  /// &lt;reference path="ZooAnimals.ts" /&gt;
  namespace Zoo {
      export class Reptile implements Animal {//Error: Cannot find Animal
           skinType ="scales";
          isMammal(){
              return false;
          }
      }
  }
  </code></pre>
  
  <p>why it shows "Error: Cannot find Animal"?</p>