parassapadaani

At Sadd I 16,5-6 there is the following comment:

tattha parassapadaaniiti parassa atthabhuutaani padaani
parassapadaani.

Does anyone have any idea what the 'attha' in 'atthabhuutaani' refers
to? Parassapadaani is translated as "active voice terminations".

Nyaasa on Kacc 406 has "parassatthaani padaani".
Kaccaayanatthadiipanii, p. 534 (Thai edn.) has "parassa atthaaya
pavattaani padaani" -- terminations occurring for another's sake ??

Is "parassa" genitive  or dative as in Skt, parasmaipadanni?

Regards,
Jim