It's a shame this is being abandoned, because if you want a rich text editor that truly is Gmail's compose editor as it has existed for the past decade - that emits the same structures that Gmail would, handles copy-pasted rich text the same way Gmail does, has the same behavior in typing inside links etc... which is especially useful if you're building an email client that Gmail users need to feel familiar on every keystroke... then following https://github.com/google/closure-library/blob/master/closur... line-for-line is still the gold standard, because it grew from the same codebase as Gmail.

I've had great success at a previous startup referencing a prebuilt Closure Library from a modern ES6+ codebase and creating a React-friendly wrapper around the editor component, and using this to power an email templating experience. Ironically, I'm within weeks of needing to do it again, thanks to Zawinski's Law https://en.wikipedia.org/wiki/Jamie_Zawinski#Zawinski's_Law - "Every program attempts to expand until it can read mail. Those programs which cannot so expand are replaced by ones which can." I'll give you one guess what I'll be reaching for, archived or not.

Others have more context on the history and have written more detailed obituaries - but it's a true testament to the engineers that worked on it, that a library can be so ahead of its time that it's still an industry-leading experience 14 years after its initial release.