While releasing 5.1.13.Final, I got a failure when building the integration guide:

rendering Book(integrationsGuide) en-US/html
Extending script classloader with the jdocbookXsl dependencies
redirecting console output to file [/home/gbadner/git/hibernate-orm-5.1.13/documentation/target/docbook/work/integrationsGuide/log/console-en-US-html.log]
Error on line 1 column 1 of http://docbook.org/xml/5.0/dtd/docbook.dtd:
Error reported by XML parser: The markup declarations contained or pointed to by the document type declaration must be well-formed.
Resetting console output
:documentation:renderDocBook_integrationsGuide_en-US_html FAILED

This can be fixed by changing "http://docbook.org/xml/5.1/dtd/docbook.dtd" to "https://www.oasis-open.org/docbook/xml/5.0b5/dtd/docbook.dtd"

in src/main/docbook/integrationsGuide/en-US/Hibernate_Integrations_Guide.xml.