Many libraries have a section entitled "Rationale". This section is very helpful for anyone who want's to use the library. The problem is that if you wait until you're done to write this section, you can't remember what the key decisions were and why you made them. That is, you don't remember all the dead ends you discarded to get your final finished product. If your library gets to review, someone will suggest that it you should of done it using method X instead of method Y
"Easy" way - don't keep notes. Here's what happens.
At some point in the development, you discover that you want to change a design decision. This means you have to use method X instead of method Y. Generally this will occur more than once during the development.
Finally you get everything done, and submit your library for review.
Now some smart guy will make a good case for using method Y instead of method X which you used. Of course you know that since you've been down that road. But now you don't remember exactly why method Y couldn't be made to work.
So you sort of fake it with a glib response which only provokes your critic to make an even stronger case. Now everything has escalated to the point where you have to go back and make a really exahaustive explanation (maybe even involving sample code!). This sucks up a huge amount of time.
"Hard" way - keep notes on your decisions as you go:
When you discover you want to change a design decision, add an explanation to your log.
Keeping such notes diminishes the possibility that you accidently change a design decision back to one that has previously been determined to be a dead end. Don't laugh - this is not hard to do!
When writing documentation, take these notes, clean them up and include them in a section called "Rationale". This makes writing this very useful documentation trivial.
Users and library reviewers will be able to see your case before they make their "suggestions". This short circuits lot's of pointless discussions. There will likely still be differences of opinion, but all the issues will be visible to all parties at the same time.