Accessing MatrixSymbol

I can't seem to figure out how to make use of the sympy `MatrixSymbol` type, described at
http://docs.sympy.org/latest/modules/matrices/expressions.html
I would like to manipulate matrix expressions on a block matrix level, not have the expressions be manipulated on the level of scalar matrix entries.

To be more specific, how do I in `SymPy.jl` create a matrix with specified dimensions, without having it be an array of scalars, like (in python)
```python
>>> X = MatrixSymbol('X', 3, 3)
>>> Matrix(X)
Matrix([
[X[0, 0], X[0, 1], X[0, 2]],
[X[1, 0], X[1, 1], X[1, 2]],
[X[2, 0], X[2, 1], X[2, 2]]])
```