Interesting technique! It's evident OpenType has some powerful applications. (One favorite is https://www.fontfont.com/how-to-use-ff-chartwell )
In a real-life scenario I would, however, be a bit concerned that you're altering the underlying text into a visual representation that is not portable -- copying the text and pasting it into another context will show the original characters.
So I would consider doing it the less glamorous well of pre-processing the text and outputting the correct characters in the first place. (Let's not go into how appropriate/ethical is to process the characters in a user's email :P)
One great use for this technique would be in programmer's font, where you could show nice curly quote, when appropriate, around strings -- and the text underneath would still have the syntactically-correct straight quotes.
That's a great example! Although I'm a bit intimidated by how much it alters the text :)
As a developer, I actually prefer that this is a loss-less transformation. One of my biggest peeves with apps that do automatic quotes by find/replace is that they become lossy channels — I paste working code in one end, and I get broken code out the other.
Maybe the right solution is to force programming languages to use ”Real Quotes“ for strings, so that it doesn't matter (though en-dashes for post-increment makes less sense...) :)
Yes, code in "prose" environments does tend to be handled poorly. E.g. https://medium.com/@kanyang/how-to-display-code-blocks-in-medium-687b3a14e47a (notice the curly quotes around the string)
You don’t “hack beautiful flourishes into font”.
You enable and access OpenType features that are already there.
You'll need to re-read the article. It entails altering OpenType features in the font itself.
You’re right. My apologies to the author…