A case affix is an °affixal °flag.
Case affixes can have the same kinds of meanings and functions as adpositions, so both are now regarded as kinds of flags. This terminology is fairly recent (Haspelmath 2005; 2019). In much of the literature, "case" is regarded as an "inflectional category/feature", and often, the "case meanings" are taken as primary.
case affix (STR) = a flag which occurs as an affix. Example: in Russian kniga Ivan-a ‘John’s book,’ -a is a Genitive case marking suffixed to Ivan ‘John.’ (Section 4.3)