The one thing from the Stripe docs I like is the embedded API key in all the code snippets, but this seems difficult to accomplish with Markdoc, especially if you're rendering the whole site to static HTML.

For example:

  ```bash
  curl https://api.example.com/stuff \
    -u {% apiKey /%}: \
    -d "foo=bar"
  ```

If the user is logged in, I want the {% apiKey /%} to be replaced with something. Do I use a transform, node, or tag to accomplish it? It seems easier to write:

  ```bash
  curl https://api.example.com/stuff \
    -u MY_API_KEY: \
    -d "foo=bar"
  ```

And then have custom JavaScript that runs on the page that does a search-and-replace for the string MY_API_KEY with the user's API key (obtained async with API, etc.). The documentation on Markdoc needs work.