The microtype package: Subliminal refinements towards typographical perfection [pdf]
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Interestingly, Guthenberg used very similar techniques with varying the shapes of letters so that the "blackness" of the page could be more uniform.
In my opinion, the default font expansion value stretch=20 is not conservative enough. I would personally recommend not only reducing it but also using the selected argument to further reduce the expansion of glyphs whose geometry distortion may be more easily perceived.
https://mirrors.ctan.org/macros/latex/contrib/microtype/micr...
Micro-typography is the art of enhancing the appearance and readability of a document while exhibiting a minimum degree of visual obtrusion. It is concerned with what happens between or at the margins of characters, words or lines. Whereas the macro-typographical aspects of a document (i.e., its layout) are clearly visible even to the untrained eye, micro-typographical refinements should ideally not even be recognisable.
However, there don't seem to be any major changes to the package since 2021. (Which is not surprising, since it was first released in 2004.)
It must be perfect!
Ohhh I see, I look it up. Apparently, it support specific feature[0] of microtype in XeLaTeX.
[0] https://tex.stackexchange.com/questions/118713/is-microtype-...