Syntax additions - converting vscode extensions?

Pretend I’m an idiot when it comes to language syntaxes in editors. I understand that Textastic is customizable but I’m still having a hard time wrapping my head around how to import/create a syntax.

I want to add Astro support to Textastic. They have language tools based on LSP (https://github.com/withastro/language-tools) but I don’t even know how to begin trying to integrate this into a syntax for Textastic.

Anyone have any examples of how they did this kind of thing from scratch?

Thanks.