Potential contributors want to know whether their contributions will be welcome. To set expectations, we should add a description of the project values to the README.md, or possibly CONTRIBUTING.md or similar.

Starting from byuu's original description on https://byuu.org/higan, I would describe the projects values (from most-important to least-important) as:

• accuracy: an emulated system should reflect the power and limitations of the original
• completeness: if the original hardware did a thing, the emulator should too, even if no known software relies on it
• code readability: somebody familiar with the emulated system should be able to look at a code fragment and understand what it does
• portability: the emulator should run on as many platforms as possible
• performance: the emulator should run games at full-speed on commonly-available hardware
• accessibility: the emulator should be easy to use, for homebrew developers and game historians as well as people who just want to play games

We would definitely welcome any and all contributions that align with these values (like emulating a new piece of hardware, or a new behaviour of existing hardware), and contributions that promote a more-important value at the expense of a less-important value (for example, increasing accuracy but decreasing performance).

We would consider contributions that promote an unlisted value (say, increased security, or use as a library).

We are unlikely to be interested in contributions that promote a less-important value at the expense of a more-important value (like performance optimisations that make the code less readable), or promote an unlisted value at the expense of a less-important value (like changes that make the software work better on one platform at the expense of others).