Cloud mask info - Organization files in S2 products

I am trying to use individual files contained in S2-L2A products to identify cloudy pixels (shades included) in the R environment.

Opening S2-L2A products in SNAP, it is quite clear which layers are correspond to dense clouds, cirrus and cloud shades. However (outside SNAP) when browsing files in the GRANULE > … > QI_DATA folder, it is not obvious at all which may correspond to the different cloud information (e.g. the “*_CLD_20m.jp2” files, but what else?).

Looking in the S2 description pages I couldn’t find details of this kind.
Anybody has an alternative reference containing this information?

Cheers and many thanks!
Francesco