Half of `doc-pl` is all bold

[alfsb]

While developing a fix for doc-pl build failures, I stubbed on this. Running:

git -C phd checkout 5f10df173f923d261fa0ae3aa3b2f5778b327e73
php zpr-doc-base/configure.php --with-lang=pl -q
php phd/render.php -d zpr-doc-base/.manual.xml -f bigxhtml

Generates thousands of:

[11:57:01 - E_WARNING             ] /home/andre/phpdoc-test/phd/phpdotnet/phd/Package/Generic/XHTML.php:1899
preg_match(): Unknown modifier '/'

PhD checkout at 5f10df because I'm stuck with PHP 8.1. zpr-doc-base is php/doc-base#277 , otherwise doc-pl wont validate.

This may be related or not with rendered doc-pl having half of the manual rendered with <strong> wrapping all tags after some point.