I was wondering if MethodOfLines allows cross derivatives. Something like this:

`Dxt = Differential(x)*Differential(t)`

My equation looks something like this:

`eq = [Dtt(F(t,x)) + 2*Dxt(F(t,x)) ~ A*Dxx(F(t,x)) + B*Dx(F(t,x)) ]`

When I ran my code, it gives me the following error message:

`Discretization failed, please post an issue on https://github.com/SciML/MethodOfLines.jl with the failing code and system at low point count.`

I am wondering if this is due to the cross derivatives. I could not find an example of cross derivatives anywhere on web and hence the query.

Thanks.