what does it take to produce a new output block

[Flaming Hakama by Elaine]

Hi,

I am interesting in seeing what it would take to enhance lilypond to output
in this text format

https://www.irealpro.com/ireal-pro-file-format

My first idea would be to add something along the lines of the midi block,
where if you add this new output, you will get output in this text format,
which is essentially an HTML link.

\score {
  … music …
  \layout { }
  \midi { }
  \ireal { }
}


I suppose it should support similar features for command line and scheme:

-direal-extension=html
#(ly:set-option 'ireal-extension "html")


To look into implementing this, where would I get started?

Is there any documentation that describes what exactly is a block, what it
takes as input, etc.?

Where would I find the code for the layout and midi blocks?


Thanks,

Elaine