Render to Djot from events

[declanvk]

Hello, thank you for the jotdown library!

I'd like to add a new Render implementation that outputs the events back to djot format.

My motivation is I've been using jotdown as part of a simple static site generator. As part of the generator, I have a couple passes which modify the content of each djot document. For example one pass will try to find a starting raw block like:

```{=json}
{
    "draft": true
}
```

And read and remove it to be used as frontmatter (since djot hasn't standardized on frontmatter yet [I think]). Right now I use the .into_offset_iter() function to find the offset of the "frontmatter" block and remove it from the original string.

The problem comes up when I'd like to write more complex transformations, like replacing symbols or rewriting links. I'd like to render the modified events back to a djot string and the re-parse if needed.

I realize an alternative would be to store the modified events in a Vec or something and modify that array before the final rendering to HTML. Let me know what your thoughts are! I can also maintain this outside of the jotdown crate to start.

Thanks again,
Declan

[hellux]

Right now I use the .into_offset_iter() function to find the offset of the
"frontmatter" block and remove it from the original string.

Yes, one way is to check where the event starts and ends and only replace that
part of the source code with your new djot output.

The problem comes up when I'd like to write more complex transformations,
like replacing symbols or rewriting links. I'd like to render the modified
events back to a djot string and the re-parse if needed.

If you wish to convert a stream of events into djot source code, it is possible
to implement a renderer that outputs djot from events. However, as mentioned in
#71, there are a few things missing from the events to allow you to reproduce
the original source code. @black-desk has implemented a renderer that takes the
events with offsets and reproduces the original source code, which may be
useful: https://github.com/black-desk/djotfmt

I realize an alternative would be to store the modified events in a Vec or
something and modify that array before the final rendering to HTML. Let me
know what your thoughts are!

Yes, if you don't need the intermediate djot source code, the easiest way is to
implement your transformations on the stream of events (either with e.g.
.map/flat_map() in a streaming fashion or on a full array) and then render the
events directly to HTML. There is also an ongoing discussion in #86 about how
to make filters composable.

I can also maintain this outside of the jotdown crate to start.

This is something that should be possible to implement using the public
interface, even if it is not within this crate we can still link to it from
here if there is a library crate that may be useful for others.