This PHP Manual build is broken

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The ru build of the PHP Manual is broken, so it does not validate or build. Please fix it! ;)

Attached is the full log

Love,
	The docs.php.net server

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===> Fri Apr 30 16:10:01 BST 2021 Starting ru
===> Fri Apr 30 16:10:01 BST 2021 Configuring ru
configure.php: $Id$
PHP version: 7.3.7

Checking for source directory... /local/src/phpdoc-git/base
Checking for output filename... /local/src/phpdoc-git//base/2021-04-30-16-ru.xml
Checking whether to include CHM... no
Checking for PHP executable... /usr/bin/php
Checking for language to build... ru
Checking whether the language is supported... yes
Checking for partial build... no
Checking whether to enable detailed XML error messages... no
Checking libxml version... 2.9.1
Checking whether to enable detailed error reporting (may segfault)... yes
Checking whether to optimize out the DTD (performance gain, but segfaults)... no
Generating /local/src/phpdoc-git/base/manual.xml... done
Generating /local/src/phpdoc-git/base/install-unix.xml... done
Generating /local/src/phpdoc-git/base/install-win.xml... done
Generating /local/src/phpdoc-git/base/developer.template.xml... done
Generating /local/src/phpdoc-git/base/scripts/file-entities.php... done
Iterating over extension specific version files... OK
Saving it... OK
Creating file /local/src/phpdoc-git/base/entities/file-entities.ent... done
Checking for if we should generate a simplified file... no
Checking whether to save an invalid .manual.xml... no
Loading and parsing manual.xml... done.
Validating manual.xml... failed.

The document didn't validate, here are the errors I got:
(If this isn't enough information, try again with --enable-xml-details)
 IDREF attribute linkend references an unknown ID "book.regex"
 IDREF attribute linkend references an unknown ID "book.regex"
 IDREF attribute linkend references an unknown ID "book.regex"

Eyh man. No worries. Happ shittens. Try again after fixing the errors above.
=============> Something happenend when snapshotting ru
Failed completely
=============> Please have a look!

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