It seems that because I used XML elements most of my post is gone and it also seems...
Issues with Docbook 5.1 CR3 RNG-based schemas
Connector works also with Saxon 9.6
Code block marked as containing CSS (but actually contains XML) breaks processing
Guarded NPE + added TC
XSLTHL breaks processing XML fragment (String Index out of Bounds)
Committed TC + small fix.