/usr/share/xml/ is in docbook-mathml 1.1CR1-2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/xml/docbook/
/usr/share/xml/docbook/custom/
/usr/share/xml/docbook/custom/mathml/
/usr/share/xml/docbook/custom/mathml/1.0/
/usr/share/xml/docbook/custom/mathml/1.0/catalog
/usr/share/xml/docbook/custom/mathml/1.0/catalog.xml
/usr/share/xml/docbook/custom/mathml/1.0/dbmathml.dtd
/usr/share/xml/docbook/custom/mathml/1.1CR1/
/usr/share/xml/docbook/custom/mathml/1.1CR1/catalog
/usr/share/xml/docbook/custom/mathml/1.1CR1/catalog.xml
/usr/share/xml/docbook/custom/mathml/1.1CR1/dbmathml.dtd
/usr/share/xml/docbook/custom/mathml/1.1b1/
/usr/share/xml/docbook/custom/mathml/1.1b1/catalog
/usr/share/xml/docbook/custom/mathml/1.1b1/catalog.xml
/usr/share/xml/docbook/custom/mathml/1.1b1/dbmathml.dtd
/usr/share/xml/docbook/custom/mathml/catalog
/usr/share/xml/docbook/custom/mathml/catalog.xml