Although the following Calc functions have a defined syntax and can be selected through the Function Wizard, the help files do not explicitly specify their syntax. - CHISQINV - GAMMA
Thank you for reporting this issue. I have set the bug's status to "minor."
Steve Fanning committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/731026465ce3b0d69c0974627037348dda4eccd0 tdf#131357 adjust Calc functions params
All changes needed to address this bug have been checked today and are fixed in the latest LibreOffice Dev 7.0 Help build. Changed status to Resolved / Fixed.
Verified, we have now explanation for them.