Is there an official API or framework for creating Squarespace editor plugins, or are most plugin authors just creating doing it from scratch?

Hello,

Plugins such as Spark or SquareKicker have great UX and almost look native to the Squarespace editor UI. I'm curious if these plugins are developed using some kind of Squarespace API (such as the elusive window.Y) to make their UI and UX look and feel native, or if they're just injecting a bunch of cleverly designed code that makes them appear as if a native editor interface?

I was thinking of creating a native-looking plugin for myself using ChatGPT API to automatically generate text for any text blocks, textareas, production descriptions, SEO, etc. (Hint hint, if this was a built-in feature for Squarespace editor it would be killer)