Hi,
BTW: all of that:
<ade:template xmlns="http://www.w3.org/1999/xhtml" xmlns:ade="http://ns.adobe.com/2006/ade" xmlns:fo="http://www.w3.org/1999/XSL/Format">
<fo:layout-master-set>
<fo:simple-page-master master-name="single_column">
<fo:region-body margin-bottom="3em" margin-top="0.5em" margin-left="3em" margin-right="3em"/>
</fo:simple-page-master>
crud is part of the Adobe "extensions" to the epub standard that are only supported by epub software running Adobe Digital Editions.
Search the web for Adobe's EPUBBestPractices-1_0_2.epub file and it details these extensions and explains how they are used.
Needless to say ... creating "extensions" for a open epub standard that only you support is not a good thing - IMHO.
All the world needs are more epubs that can only be read on one specific reader ... yeah right!
Hope this helps,
Kevin