[sramam]

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.....

[rtpg]

The depth here can be context dependent. For example if you had a bunch of brackets and parens in your grammar, you might only care about paren depth. Or if your language had brackets and parens and function definitions, your "expression depth" might ignore function definitions (or even reset at a function definition boundary if you have inner functions!)