Is there documentation on how mtail's runtime and parser are implemented?

Hi mtail team,

Thanks for your work on this project — it’s been really useful for log-based metric extraction.

I'm curious about the **implementation details of mtail's runtime**, particularly:

* Is the mtail language parser and runtime based on any existing libraries (e.g., lex/yacc, ANTLR, PEG, etc.)?
* Or is it entirely custom-built?
* Are there any documents, design notes, or blog posts that explain the architecture, especially how mtail programs are parsed and executed?

I’m asking because I’d like to better understand the limitations, performance characteristics, and possibly contribute in the future.

Appreciate your insights!