Hmm, funny thing, my ZHLT folder (installed together with Radiant) was missing the Readme.txt file. It seems to me I've been using some obsolete version of Zoner's Tools:
CCXX32.dll
clipnode.map
default.hull
dumpbrush.pl
dumpent.pl
dumpline.pl
hlbsp.exe
hlcsg.exe
hlrad.exe
hlvis.exe
netvis.exe
netvis.html
numberbrush.pl
ripent.exe
stripnulents.pl
tfcabbrev.pl
zeditor.wad
zhlt.css
zhlt.wad
ZHLTIntro.html
ZHLTProblems.html
ZHLTReference.html
ZonersHalflifeTools.html
I've now the latest version - together with Readme file.
Thank's for the info, Andy!