Paniniya Shiksha, certainly a text by Maharshi Pāṇini. Shiksha refers to Dhvanishastra or Phonetics. It’s also a science of phonemes(dhavani). Since Sanskrit is a scientific language, every letter, phoneme has its significance; separate meaning. The meaning varies accordingly and if used otherwise, gives wrong result and if it is a technical literature like Veda, Tantra etc., then it’s a grievous one with serious repercussion. The verse quoted below shows an incident where it has given a wrong result with wrong usage:

“Mantrahinanaḥ svarato varnato vā mithyāprayukto na tamarthamāha / Sa vāgvajro yajamānam hinasti yathenraśatr̥rsvarato’parādhāt//"

That is why right pronunciation of words is very important to arrive at right result. On account of this, Panini has very clearly explained all these aspects under this text and this is what it is called Paniniyashiksha.