On Thu, Feb 28, 2019 at 11:57:01AM +0100, Frank Mittelbach wrote:
true, but it is also correct that in the last 3 decades essentially any font usable with TeX (well LaTeX) had the ligatures, so the statement in the TeX book that --- is the way to get an emdash was/is true with virtually all fonts in use in pdftex. So it is not just a quirk of CM fonts, it is largely a feature of the ecosystem (or was in the days of Type 1 fonts) and as such it is a pity imho if it becomes a breaking change when processing a document with a unicode engine.
But the engines didn’t change at all in that respect: the actual change that XeTeX and LuaTeX brought is that all of a sudden it became possible to use many more fonts than before, most of which didn’t have the ligatures that TeX users had come to expect. Arthur