Q:

How can I slice one plane from a VectorPlot3D to get a stream plot?

I am analyzing a system of ODEs in three equations/three variables, and I have a linearized system
$$\begin{bmatrix} x' \\ y' \\ z' \end{bmatrix} = \begin{bmatrix} -1 & -1 & 0 \\ 0 & 2 & 0 \\ 0 & 0 & 1 \end{bmatrix} \begin{bmatrix} x \\ y \\ z\end{bmatrix}.$$
I have plotted this in 3D using VectorPlot3D and I would like to get slices, i.e., stream plot representations of the XY, XZ, and YZ planes. If the equations were completely decoupled I would just make three separate plots using the StreamPlot` -- however, the equations for $x'$ and $y'$ are only partially decoupled, so I am not sure how to get a 2-Dimensional stream plot on the XZ plane, as I can only specify two variables.
So, is there a way to input my 3D vector field equations and get out 2D slices on certain planes? I think I can do this using either the ViewPoint or ViewProjection options, but I am not sure how to use them.
Here is my VectorPlot3D code for reference.
VectorPlot3D[{-x - y, 2 y, z}, {x, 0.0, 1.2}, {y, 0.0, 1.2}, {z, 0.0, 1.2},
  Axes -> True,
  AxesLabel -> 
    {Style["x", Bold, FontSize -> 24], Style["y", Bold, FontSize -> 24],
     Style["z", Bold, FontSize -> 24]},
  VectorColorFunction -> "Rainbow",
  VectorPoints -> 5,
  VectorScale -> {0.1, .7, None}]

A:

I realized that the definition of the XZ plane is that $y=0$ for all coordinates lying on the plane. So, I can plot the XZ plane as
StreamPlot[{-x, z}, {x, 0, 1.2}, {z, 0, 1.2}]. And this is exactly the same as taking a slice of the 3D vector field.

