It has confused me for years. The left and right sides of a splitter depend on the splitter orientation. I never select them right from the first try
![Smile :)](./images/smilies/icon_e_smile.gif)
it is ok when a splitter is oriented from bottom to top, and is the opposite when a splitter is oriented from top to bottom. In vertical orientation, it is even worse.
Maybe it is better to call inputs and outputs in some side-agnostic way like A and B?