sarvam etad varṇeṣvapi kalpayituṃ śakyata iti darśayann āha varṇeṣvityādi / varṇeṣu śakyate ceyaṃ pratyabhijñā vināśiṣu /
All this can be conceived in the case of letters also, as [the author] shows when saying "varṇeṣu" etc. This recognition is possible in the case of perishable letters.