Most kerning in Latin fonts involves diagonal or overhanging shapes., i.e. the shapes that are exceptional to the straight-straight, round-round, and straight-round relationships that determine the default spacing.
The only times you should ever find yourself kerning a straight to a round is an uppercase straight being followed by a lowercase round, which in some designs might benefit from being slightly tightened.
When I'm kerning, I look at everything, including straight-straight, etc. in context of words, because its a process that I find useful to confirm default spacing. But when I examine the results in the kerning, I typically see the same set of kern pairs involving diagonals and overhang shapes.
How many "kern pairs" did some of the most famous letterpress types have?
None. And diagonal and overhang shapes produced big gaps within words. We can do better.
[My IUC39 presentation Beyond Shaping provides an overview of the steps involved in text processing and display with OpenType, which might be helpful in making sense of the issues raised in this thread. Yes, there are multiple shaping/layout engines at play — with some inconsistencies as noted in the presentation —, but they all follow basically the same overall model.]
Hrant, as someone who almost always disagrees with you but sometimes values your input, I hope you won't be offended if I point out that there's a steady decline in the quality of your discourse over the course of this thread, with your last post consisting of little more than a series of slogans. You can do better than this, and I'm afraid you'll have to if you want to continue a conversation. I find absolutely no value in talking to you when you're being like this.
Very much earlier than that, I think. I don't recall seeing the rounded р in any 19th Century Russian text faces — which is not to say that they don't exist, only that the seriffed form seems to have become the primary model well before the 20th Century. Indeed, I wonder if the rounded form made it until the end of the 18th?