Say I want to define that an URI such as:
myapp://path/to/what/i/want?d=This%20is%20a%20test
must be handled by my own application, or serv
I strongly recommend that you not define your own scheme. This goes against the web standards for URI schemes, which attempts to rigidly control those names for good reason -- to avoid name conflicts between different entities. Once you put a link to your scheme on a web site, you have put that little name into entire the entire Internet's namespace, and should be following those standards.
If you just want to be able to have a link to your own app, I recommend you follow the approach I described here:
How to register some URL namespace (myapp://app.start/) for accessing your program by calling a URL in browser in Android OS?