Before revision:  We derive their order conditions up to third order, and show that such methods can preserve positivity (and more generally strong stability) with a time-step restriction  independent of the stiff term , under mild assumptions on the operators.
After revision:  We derive their order conditions up to third order, and show that such methods can preserve positivity (and more generally strong stability) with a time-step restriction is independent of the stiff term , under mild assumptions on the operators.