The LEGO EV3 Block Developer Kit documentation refers to these as "gray blobs". These are compiler intrinsics and don't have a .vix implementation. They generally correspond directly to the bytecodes from the EV3 Firmware Developer Kit.
Note: Developer kits are available on the official LEGO MINDSTORMS download page.
So I ended up figuring out a solution:
First, I tried manually editing the vix file as a text file, and inserting this code.
Opening this file would crash the software.
However, if you didn't open it, it would work fine on the EV3 brick!
From this, I concluded, that the problem is with the EV3 vix editor.
But identifying the problem wasn't enough, I needed ...