Hi, it seems that Boost fails building boostbook docs if xsltproc and libxslt1 version 1.1.35 is installed (it works with version up to 1.1.34). Specifically, I can reproduce the failure following these steps: * recursively clone git@github.com:boostorg/boost.git * ./bootstrap.sh * echo "using boostbook ;" > user-config-doc.jam * ./b2 -j32 -q -d2 --ignore-site-config --enable-index --user-config=user-config-doc.jam --build-dir=build-doc * ./b2 -j32 -q -d2 --ignore-site-config --enable-index --user-config=user-config-doc.jam --build-dir=build-doc doc On my Debian unstable system this works when xsltproc and libxslt1.1 version 1.1.34 are installed, but fails when 1.1.35 is installed, with the following error: "xsltproc" --stringparam boost.defaults "Boost" --stringparam boost.root "../../../.." --path "build-doc/boost/bin.v2/libs/logic/doc/docbook" --xinclude -o "build-doc/boost/bin.v2/libs/logic/doc/docbook/tribool.docbook" "/<<PKGBUILDDIR>>/tools/boostbook/xsl/docbook.xsl" "/<<PKGBUILDDIR>>/libs/logic/doc/tribool.boostbook" runtime error: file /<<PKGBUILDDIR>>/tools/boostbook/xsl/annotation.xsl line 432 element element xsl:element: The effective name '' is not a valid QName. runtime error: file /<<PKGBUILDDIR>>/tools/boostbook/xsl/annotation.xsl line 432 element element xsl:element: The effective name '' is not a valid QName.runtime error: file /<<PKGBUILDDIR>>/tools/boostbook/xsl/annotation.xsl line 432 element element xsl:element: The effective name '' is not a valid QName. [repeated many times] Many different libraries are failing in the same way, so I guess that the real problem is in boostbook. However I don't know enough of XSLT and xsltproc to give a proper diagnosis. For the context, this bug was discovered during a test rebuild of the Debian package for Boost[1]. However it can be reproduced with master doing the steps above. [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1016321 Thanks in advance for any help you can provide, Giovanni.