What subspaces of n-tuples of rational functions can be the solution space to a system of differential equations?

Let $K=mathbb{C}(x)$ denote the field of rational functions (in 1 variable), and let $K^n$ denote an $n$-dimensional $k$-vector space (with basis). For some integer $m$, let
$$delta_{11}, delta_{12},...delta_{1n};delta_{21},delta_{22}...delta_{2n};...;delta_{m1},delta_{m2},...delta_{mn}$$
be $mn$-many differential operators in $x$ with coefficients in $K$, so that
$$ delta_{11}(f_1)+...+delta_{1n}(f_n)=0$$
$$ delta_{21}(f_1)+...+delta_{2n}(f_n)=0$$
$$...$$
$$ delta_{m1}(f_1)+...+delta_{mn}(f_n)=0$$
defines a system of $m$-many differential equations on $(f_1,...f_n)in K^n$. Let $Ssubseteq K^n$ denote the space of solutions to this system of differential equations; by homogeneous linearity it is a $mathbb{C}$-subspace of $K^n$.

Usually, people are interested starting with a system of equations and finding the solution space. I have a weak inverse question. When is a given $mathbb{C}$-subspace $Vsubseteq K^n$ the solution space to such a system of differential equations? I don't care (yet) about finding the system of equations or how many equations there are, only whether they exist.

For $n=1$, the answer is appealingly simple. Either the system is degenerate, and the solution space is all of $K$; or it is not, and the solution space is finite $mathbb{C}$-dimensional. Therefore, an infinite $mathbb{C}$-dimensional proper subspace of $K$ is not the solution space to any system of equations, and every finite $mathbb{C}$-dimensional subspace is the solution space of some system (I believe, I have not checked).

I am interested in similar results for larger $n$. I suspect that there are similar `small or everything' type results, but I don't know what a good guess for what small might be. Note that any $K$-subspace of $K^n$ is a solution space, with defining equations given by a matrix over $K$ with that space as the kernel.