title: What is the correct way to write Excel UDF's so they work on Desktop, Web and Mobile Office
body: <p>With the introduction of Excel on Android and iOS, I'm not sure what's the correct method of creating a UDF (User Defined Function) that will work across all versions of the Office 365?</p>
  
  <p>I want my UDF to work on iPad, Android as well as Desktop. What's the official Microsoft way of supporting all of these versions of Office for UDF's?</p>