The current implementation of the logic for CASE and CASEINLINE for 'sys' selector is wrong. Default case/caseinline cannot be WIN. It depends on the other cases of the page. E.g. If URL sends &System=WIN and the page has a case inline only for UNIX, then WIN must display the default. Note: only one 'sys' can be visible in the rendered page.
Sample case https://help.libreoffice.org/6.0/en-US/text/shared/guide/digitalsign_send.html?System=UNIX&DbPAR=SHARED#bm_id7430951 In this page the section "Manage your certificates" is not shown.
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/help/commit/?id=13098ccef163c813ae3e196511f44a16a6e73fdd tdf#116150 Fix logic for case/caseinline with 'sys'
fix is broken. Need reopne
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/help/commit/?id=d5ca87f12819b669646bb6f0978f79ebb5d3f035 tdf#116150 Review XHP <switch> style transform