Google Docs also does these replacements.

> I was under the impression that you do "-" for hyphen, "--" for En dash, and "---" for Em dash. IIRC, LaTeX (or maybe the editor, it has been some time) even helpfully changes that for you to the correct dash.

The conversion of '--' to an en dash and '---' to an em dash is done by the TeX compiler, and appears in the rendered file, but I think that most TeX editors don't change the TeX code itself. (This is distinct from XeTeX-based compilers, which can handle non-ASCII Unicode characters like the em dash '—' directly in the source.)

(I think that the article's point is that, in some fonts, -- (two hyphens) is literally the (approximate) size of an em dash, not that it is always understood as meaning an em dash. At least in my font, --- (three hyphens) is far too long to literally look like an em dash:

---

--

—

–

(in order, three hyphens, two hyphens, em dash, en dash).)