can the toc.ncx playOrder series have gaps in it ?
for example, I'm thinking about using the form 123456 for my books where 1 is the literal number 1, 23 is the book number in the series, 4 is a code for 0=title page, toc, prologue, etc. 1=chapters of the book, and 2= anything after the chapters.. so book 2 chapter 14 would look like 102114, but there might not be anywhere near 102114 entries before it (probably only 17 or so). is this valid, or do all the toc.ncx playOrder entries need to be perfectly sequential (1, 2, 3, 4, 5, etc..)
thanks in advance
