@pimms.param<EOL><INDENT>def mesh(m):<DEDENT>
if m is None: return None<EOL>if not isinstance(m, Mesh):<EOL><INDENT>raise ValueError('<STR_LIT>')<EOL><DEDENT>return pimms.persist(m)<EOL>
proj.mesh is the mesh on which the given projection was performed; this mesh should be a 3D
spherical mesh. If proj.mesh is None, then this projection has not yet been reified with a
mesh object.