/usr/share/boostbook/ is in libboost1.65-tools-dev 1.65.1+dfsg-0ubuntu5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/boostbook/dtd/
/usr/share/boostbook/dtd/1.1/
/usr/share/boostbook/dtd/1.1/boost-no-inspect
/usr/share/boostbook/dtd/1.1/boostbook.dtd
/usr/share/boostbook/dtd/boostbook.dtd
/usr/share/boostbook/xsl/
/usr/share/boostbook/xsl/admon.xsl
/usr/share/boostbook/xsl/annotation.xsl
/usr/share/boostbook/xsl/callout.xsl
/usr/share/boostbook/xsl/caramel/
/usr/share/boostbook/xsl/caramel/LICENSE
/usr/share/boostbook/xsl/caramel/concept2docbook.xsl
/usr/share/boostbook/xsl/caramel/cpp-operators.xml
/usr/share/boostbook/xsl/caramel/unparser.xsl
/usr/share/boostbook/xsl/chunk-common.xsl
/usr/share/boostbook/xsl/docbook-layout.xsl
/usr/share/boostbook/xsl/docbook.xsl
/usr/share/boostbook/xsl/doxygen/
/usr/share/boostbook/xsl/doxygen/collect.xsl
/usr/share/boostbook/xsl/doxygen/doxygen2boostbook.xsl
/usr/share/boostbook/xsl/dtd/
/usr/share/boostbook/xsl/dtd/dtd2boostbook.xsl
/usr/share/boostbook/xsl/error.xsl
/usr/share/boostbook/xsl/fo.xsl
/usr/share/boostbook/xsl/function.xsl
/usr/share/boostbook/xsl/global.xsl
/usr/share/boostbook/xsl/html-base.xsl
/usr/share/boostbook/xsl/html-help.xsl
/usr/share/boostbook/xsl/html-single.xsl
/usr/share/boostbook/xsl/html.xsl
/usr/share/boostbook/xsl/index.xsl
/usr/share/boostbook/xsl/library.xsl
/usr/share/boostbook/xsl/lookup.xsl
/usr/share/boostbook/xsl/macro.xsl
/usr/share/boostbook/xsl/manpages.xsl
/usr/share/boostbook/xsl/navbar.xsl
/usr/share/boostbook/xsl/reference.xsl
/usr/share/boostbook/xsl/relative-href.xsl
/usr/share/boostbook/xsl/source-highlight.xsl
/usr/share/boostbook/xsl/template.xsl
/usr/share/boostbook/xsl/testing/
/usr/share/boostbook/xsl/testing/Jamfile.xsl
/usr/share/boostbook/xsl/testing/testsuite.xsl
/usr/share/boostbook/xsl/type.xsl
/usr/share/boostbook/xsl/utility.xsl
/usr/share/boostbook/xsl/xhtml.xsl
/usr/share/boostbook/xsl/xref.xsl