IPDs are a shrink-to-fit description of larger scale (in either code size or impact) project wishing to make changes to illumos. They should describe the what and the why and give people the opportunity to comment on both.
An IPD is at its heart, just a README.md in a numbered directory in this repository, existing IPDs are enumerated below for easy reference. Further information is available at the end of this document.
Contributions are welcome. A good rule of thumb as to whether you should have an IPD is whether you are making a change with high impact to other developers or users (introducing or removing a supported platform, doing something with non-obvious compatibility constraints), or engaging in a long-term project that will likely integrate in pieces, to provide the overall picture.
For your first contribution, you might want to just submit a pull request to this repository. Going forward if this is a thing that you will do again, we'll probably give you write access to this repository so you can just add your new IPDs as they come up.
An IPD has a short header block indicating authorship (that's you), sponsorship (we'll get to that), and state.
You've started writing your IPD and you want to share it narrowly, or even just to reserve your a number in this repository. You're predraft, maybe you only have a title and a short paragraph right now, that's fine.
You've finished writing and explaining, and now you're going to send your IPD to the developer mailing list, this is a draft, you're going to receive feedback so it's not complete, but it's close.
One or more people from the illumos core team have agreed that what you've described is a good thing, and that we should do it. Your IPD is done and published (though is not immutable! If you find more information would be useful later, please add it!)
"Sponsor" is a weird word here, it's just the person or people on the illumos core team who were ok with your IPD. Don't worry about it.