Notebooks and page numbers

[Jeff Clough <jeff chaosphere com>]

Reading the docs, it looks like every page of a notebook has a
zero-based index number I can easily retrieve.  It also look like there
are ways to re-order the pages in a notebook which may, or may not,
change the indexes of these pages.

What are the "rules" as to how these pages are numbered and how those
numbers can be altered?  If I have four pages and the second one gets
removed, do I now have pages with indexes 0, 1 and 2?  Are there any
situations where the numbers of these pages would be changed out from
under me?  Any guidance here would be great.

Jeff