I've noticed some inconsistencies in the way Oxygen validates a chapter element in an xinclude file when you add xml:id= I have . I'm trying to add xml:id to chapters so I can change the output html with the use.id.as.filename parameter. I'm using xincludes with each separate xinclude file containing a chapter. I'm getting a weird error message when validating in Oxygen. SystemID: I:\My Documents\xml\rj3\er1.xml Engine name: oNVDL Severity: error Description: bad value for attribute "id" from namespace "http://www.w3.org/XML/1998/namespace" Start location: 2:80 ******************************* here is what I have in the er1.xml file: <?xml version="1.0" encoding="UTF-8"?> <chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="99er1"> <title xml:id="firstdd">Notion #1</title> <para xml:id="blah">ddddd</para> <para>Designed by Gustave Eiffel in 1889,<parameter ></parameter> The Eiffel Tower is one of the most widely recognized buildings in the world. </para> </chapter> Ok, now for the freaky part. If I remove xml:id attribute, rename the chapter element to sect1 and insert xml:id again, it validates just fine. I've tried it several times and can duplicate it each time on my machine. I've tried the Reset Cache and Validate option each time. Any idea if this is an Oxygen/validator bug or if there is something peculiar to xinclude syntax which I am overlooking? Any reason why this corrects the problem? By the way, sometimes it can be difficult to tell whether a problem is an application-specific problem or a docbook/xsl problem. Thanks. Robert -- Robert Nagle 12777 Ashford Point Dr #1417 Houston, Texas 77082 713 893 3424 htpt://www.robertnagle.info