[1] Help users find your app with MIME type-based Chrome Web Store marketing - Google Apps Developer Blog ( 版) <http://googleappsdeveloper.blogspot.jp/2012/08/help-users-find-your-app-with-mime-type.html>
Though the type field accepts only MIME types, it allows you to model file extensions as the special type application/vnd.google.drive.ext-type.<EXTENSION>.
[2] Help users find your app with MIME type-based Chrome Web Store marketing - Google Apps Developer Blog ( 版) <http://googleappsdeveloper.blogspot.jp/2012/08/help-users-find-your-app-with-mime-type.html>
"type": ["application/vnd.ms-project",
"application/vnd.google.drive.ext-type.mpp"],
[3] Create a Chrome Web Store Listing | Drive REST API | Google Developers ( 版) <https://developers.google.com/drive/web/listing>
The recommended best practice for Drive is to register both MIME types and file extensions. Though the type field accepts only MIME types, it allows you to model file extensions as the following special type:
application/vnd.google.drive.ext-type.<EXTENSION>