How do you rewrite all nested objects based on surrounding context?

[rvadhavk]

In CSS, you can do something like

div[data-foo="a"] > a[data-bar="b"] {
  color: red;
}

to rewrite a matching node to set the color property.

Similarly, in Meander, I'd like to take a map like

{
  :a {
    :foo "a"
    :bloop 3
    :b {
      :bar "b"
     }
}

and rewrite all nodes matching {:bar "b"} in the map if they have a parent matching {:foo "a"} to add the key-value pair {:color "red"}

{
  :a {
    :foo "a"
    :bloop 3
    :b {
      :bar "b"
      :color "red"
     }
}

I've been spending a bit of time trying to figure out how to make this work with m/rewrite and m/$, but I'm not sure if that's the right approach.