What is India-Pakistan 'Lahore Declaration' pact that Pakistan admits to violating?

Ex-Pakistan PM Nawaz Sharif admitted to violating the Lahore Declaration peace agreement with India that was signed in 1999 by Sharif and ex-India PM Atal Bihari Vajpayee. The treaty was signed to avoid accidental and unauthorised use of nuclear weapons after both India and Pakistan performed nuclear tests in 1998. Pakistani forces infiltrated into Kargil soon after, leading to war.