Also, I noticed that it requires WebGL so without modern and supported by WebKit graphic card it won't work. Why is OpenGL necessary for a text editor? I don't understand.
Why not? Modern desktops are all hardware-accelerated anyway.
They will render text to a bitmap using HTML canvas and then use that as a texture for GPU.
GPU will be compositing those bitmaps, it won't actually be rendering text.
I've written a OpenGL engine for a university course that use partial frame updates to reduce the number of redraws per frame.
IIRC the partial rerender variant was about 3 times faster than the full render.
try drawing a 5k monitor full of true type fonts in software sometime.
Things like filling rectangles or scrolling have been hardware optimized for years on Windows without using any OpenGL and it works even on ancient graphic cards. So I think it might be a better technology for a text editor.
Yes - for example, Apple has been shipping 5K 27” displays in iMacs for three years now.
You struggle to find a 5K display outside that one machine that Apple doesn't seem all that fussed about compared to their laptop and iOS offerings.