As high-performance computing (HPC) machines become increasingly complex, middleware-based programming paradigms have been particularly successful in reducing code development time and increasing simulation efficiency. The parallel particle-mesh (PPM) library is a state-of-the-art HPC middleware for parallel particle-mesh simulations. It is based on a concise set of six data and operation abstractions. The present paper describes the architecture of the new PPM library core. This new core architecture enables several simplifications in the library's user interface and supports for the first time the implementation of multi-resolution simulations using PPM. We further demonstrate the competitive performance of the new core architecture compared to the previous version of the PPM library.