There are many places where the boostbook xml/xsl files make reference to external files that we have no control of. Here is an example from modular-boost/tools/boostbook/xsl/docbook.xsl <?xml version="1.0" encoding="utf-8"?> <!-- Copyright (c) 2002 Douglas Gregor <doug.gregor -at- gmail.com> Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xi="http://www.w3.org/2001/XInclude" version="1.0"> <xsl:import href="http://docbook.sourceforge.net/release/xsl/current/common/common.xsl"/> <xsl:include href="reference.xsl"/> ... This means that if something changes in docbook.sourceforge.net/release/xsl/current/common/common.xsl We'll have problems when we try to build documentation. This recently happened to me and it was a bitch to find. I spent some time looking around for the right way to fix this and came upon the concept of XML catalogs as explained here: https://en.wikipedia.org/wiki/XML_catalog#Example_Catalog.xml Seems to me that the maintainer of boostbook should verify that my understanding is correct and update boostbook files accordingly. Actually, I'd be grateful to any insight on this subject that anyone might provide. Robert Ramey