  A timely and long-term programme of kaon decay measurements at a new level of
precision is presented, leveraging the capabilities of the CERN Super Proton
Synchrotron (SPS). The proposed programme is firmly anchored on the experience
built up studying kaon decays at the SPS over the past four decades, and
includes rare processes, CP violation, dark sectors, symmetry tests and other
tests of the Standard Model. The experimental programme is based on a staged
approach involving experiments with charged and neutral kaon beams, as well as
operation in beam-dump mode. The various phases will rely on a common
infrastructure and set of detectors.
