The diagonal reflection principle

We introduce a highly simultaneous version of stationary set reflection, called the Diagonal Reflection Principle (DRP). We prove that $PFA^{+\omega_1}$ implies DRP, and DRP in turn implies that the nonstationary ideal on $[\theta]^\omega$ condenses correctly for many structures. We also prove that MM implies a weaker version of DRP, which in turn implies that the nonstationary ideal on $\theta \cap$   cof$(\omega)$ condenses correctly for many structures.