[Question] How do I define a fallback function for external functions?

[rockobonaparte]

I have this test script for experimenting with embedding the engine with a Unity project I am doing:
[It seems like the "insert code" formatting is choking on the script, but I assume you can see what I'm doing]

EXTERNAL multiply(x,y)

- Hello world!
*   Hello back!
    - - Yay!
*   Derp Derp!
    - - What?

- Well, Nice to hear from you! Fun fact: 2 x 2 = {multiply(2, 2)}
-> END

It works fine in-game. The Ink editor is angry about that multiply function though:
Ink.Runtime.StoryException: Missing function binding for external 'multiply', and no fallback ink function found.

I mean, of course it would complain. It's externally defined! But I was intrigued by defining a fallback ink function so I could keep getting syntax help from the editor--instead of it choking on that whenever I type anything. I didn't see that mentioned in the documentation, namely:

https://github.com/inkle/ink/blob/master/Documentation/RunningYourInk.md#exernal-functions

It implies this is a thing I can do, so I'd like to know how that's done.

[joethephish]

It should just be a matter of creating an ink function with the same name / declaration. So, if you have EXTERNAL multiply(x,y) at the top of your ink file, make sure you have something like:

== function multiply(x,y) ==
~ return 1 // placeholder result

[rockobonaparte]

That looks to have done it, but it wasn't happy with the function declaration unless I stuffed it at the bottom of the file, for whatever reason.