The principle resource is the Unicode Home Page.
Within that page, the downloadable version (in PDF format) of the book The Unicode Standard
explains most issues in exhaustive detail. Actually, it is a very good read if you are interested
in writing systems of the world, even for the non-computer-literate reader.
The Unicode Standard does not document all of Unicode. There are also Standard Annexes.
The most important one for this topic is annex #15:
Unicode Normalization Forms.
Also of relevance to this library (but not yet implemented) is technical standard #10
Unicode Collation Algorithm.
