How do splitters work?

I scrolled through the sub quite a bit,but couldn't find anyone asking this.

Imagine a splitter with 3 belts hooked up to it (one to each output). How does the splitter decide what belt receives a material first? I have multiple theories how it could work, however I am currently unable to test it.

A- Attachment order, the splitter distributes the materials in the order which the belts got attached to it. B- A set order: left to right, right to left or mid to etc. C- A third way I didn't think of.

I have been trying to plan an automated production, while I am unable to play the game and found myself stuck wondering about that.

Edit: To be safe, each belt would carry the same item. Edit: I did not want to reveal for what exactly I needed this, as I wanted to figure it out on my own. But I am trying to develop an algorithm that would consistently give me 3 out 5 incoming plates.