# Square bracket notation in equation

I'm attempting to understand a paper[1] on contracting geometry for computer graphics. I have an undergraduate Physics degrees to give some indication of my experience, though that was 6 years ago now.

I'm stumbling on a basic part as I'm unfamiliar with the notation:

$$\begin{bmatrix} \mathbf{W}_L\mathbf{L} \\ \mathbf{W}_H \end{bmatrix}\mathbf{V}' = \begin{bmatrix} 0 \\ \mathbf{W}_H\mathbf{V} \end{bmatrix}$$

Were to blindly guess I'd suggest it was shorthand for specifying:

$$\mathbf{W}_L\mathbf{L}\mathbf{V}' = 0$$ and $$\mathbf{W}_H\mathbf{V}' = \mathbf{W}_H\mathbf{V}$$

But then I'm confused by the relevance of the second equation in the context.

I don't know if I've provided enough information. Happy to provide more if desired.

-