@mhoye What's interesting is that all of those would've worked in #Elisp without ever leaving #Emacs.

Much of it with #CommonLisp and #SLIME too. Most of the implementations also come with #info #manuals and their source-code (for those things not mentioned in the manual), and hyperspec.el also handles searching through the #HyperSpec locally on one's machine (it's packaged on Debian) and provides keybinds to search symbols automatically right from your editor.

C lacks most of this.