1. http://www.sagehill.net/docbookxsl/IndexOutput.html (page 312)
Here it says: "Characters such as a, à, and ä should sort together, but they do not."
This needs some clarification, since it varies a lot between languages. For example, Swedish has a (U+0061) and ä (U+00E4) characters, and they should not be sorted together.
2. http://www.sagehill.net/docbookxsl/Chunking.html#ControllingChunks (pages 67-68)
Quote: "When you use this process, you must have an id attribute on every element that you want to start a new chunk. This includes the document element, which generates the title page and table of contents. You can see which elements do not have an id by examining the generated TOC file and looking for empty id attributes in the tocentrys."
As far as I can tell, there is no need to have id attributes on every element that should start a new chunk. If there are no IDs, they are autogenerated (and btw, the tocentrys don't have id attributes; they have linkend attributes.)