Emacs is quite discoverable, too. Spacemacs even more, I think.

Yup. It's called a "self-documenting editor" for a reason :). From built-in help on every command, function, variable and keybinding, through apropos and tutorial, through a full-length manual - all available off-line, in the editor - it's easy to get your bearings around using and customizing Emacs. That is, once you adopt the old-school, pre-web notion of software actually having documentation.

It's right there in the toolbar, the "P"-ish looking icon.

You mean the paragraph mark, "¶"? The Show All feature in Word will highlight whitespace, tabs, newlines, which is helpful. But in WordPerfect, Reveal Codes would show much more than that: style changes, image and table introductions, etc. It was much more like looking at the HTML source of a Web page in a Web Developer tool -- not only could you see the tags, but you could modify and remove them easily and precisely.