This is so cool.

Question (caveat: first export to treesitter and tools like this): Is there a reason the example demonstrates the use of depth as a variable instead of it being built in?

Nesting level of a particular "type" is general enough that it might be included OOTB. What you want to do with this might be generalizable - for example instead of

```

    enter section {
        depth += 1;
    }
    leave section {
        depth -= 1;
    }

    enter atx_heading {
        print("<h");
        print(depth);
        print(">");
    }
    leave atx_heading {
        print("</h");
        print(depth);
        print(">\n");
    }

```

It could simply be:

```

    enter atx_heading {
        print("<h");
        print(depth);
        print(">");
    }
    leave atx_heading {
        print("</h");
        print(depth);
        print(">\n");
    }

```

So depth is always of the nested levels of the same node type, but available out of the box. For markdown, it's headings, sections and lists come to mind - but I might be wrong.

In any event, this looks really well thought-out and now to checkout the other tools mentioned in the comments.....