This is a bit tedious. The trick is to add new matrix elements (cells) where you insert your "decorations". Here's what it looks like:

The formula is structured as:

```
left [ -- left outer bracket
matrix { -- outer matrix
matrix { left [ { a # b ## c # d } right ] -- NW element
# dotsvert -- fake top center element
# left [ B right ] -- NE element
## dotsaxis # ` # dotsaxis -- fake center row
## -- next row
left [ C right ] -- SW element
# dotsvert -- fake bottom center element
# left [ D right ] -- SE element
} -- close outer matrix
right ] -- right outer bracket
```

I added comments with `--`

, but this is not part of Math syntax.

Eventually, you can "dim" the dots with `silver attributes`

if you find them too bold.

*To show the community your question has been answered, click the ✓ next to the correct answer, and "upvote" by clicking on the ^ arrow of any helpful answers. These are the mechanisms for communicating the quality of the Q&A on this site. Thanks!*