Neovim highlights are extmarks
While trying to contribute to nvim-ts-rainbow I discovered that highlights in Neovim are implemented using extmarks.
Neovim is a modern extensible vim-based text editor. I switched to it from Visual Studio Code and use it as my main text editor/IDE. The main differentiators are the fact that Neovim allows configuring it and writing plugins in Lua, as opposed to the Vimscript language.
While trying to contribute to nvim-ts-rainbow I discovered that highlights in Neovim are implemented using extmarks.