code. The implicit solver itself should remain agnostic to the specifics of the Blender data (cloth vs. hair). This way we could avoid the bloated data conversion chain from particles/hair to derived mesh to cloth modifier to implicit solver data and back. Every step in this chain adds overhead as well as rounding errors and a possibility for bugs, not to speak of making the code horribly complicated. The new subfolder is named "physics" since it should be the start of a somewhat "unified" physics systems combining all the various solvers in the same place and managing things like synchronized time steps.