Reflectance quantity in Sentinel-2 Level-2A products?

What is the used reflectance quantity in the S2 Level-2A products? Is it the bidirectional reflectance factor (BRF) or the hemispherical-directional reflectance factor (HDRF).

And how is this obtained?

Thank you in advance!

(I’m referring to the reflectance quantities are explained by Schaepman-Strub et al. 2006. DOI: 10.1016/j.rse.2006.03.002)