Although the concept of a type is fairly unambiguous, models need additional information to deal with the type. Conditions provide this information. For example, with a boundary of type wall, the conditions will tell us whether this is to be a no-slip wall, a slip wall or a moving wall. The conditions will also tell us whether we want to apply a specified temperature (Dirichlet) thermal boundary condition or a specified heat flux (Neumann) thermal boundary condition.