* Add variant selectors for lowercase Greek Pi (`π`) and Tau (`τ`) (#1924).
* Add characters:
  - CYRILLIC SMALL LETTER ROUNDED VE (`U+1C80`).
  - CYRILLIC SMALL LETTER TALL TE (`U+1C84`) (#1911).
  - CYRILLIC SMALL LETTER TALL HARD SIGN (`U+1C86`) (#1911).
  - CYRILLIC SMALL LETTER TALL YAT (`U+1C87`) (#1911).
  - LEFTWARDS OPEN-HEADED ARROW (`U+21FD`) ... LEFT RIGHT OPEN-HEADED ARROW (`U+21FF`) (#1912).
  - DIAMETER SIGN (`U+2300`) (#1923).
  - CIRCLE WITH SUPERIMPOSED X (`U+29BB`).
  - LEFTWARDS TWO-HEADED ARROW WITH TRIANGLE ARROWHEADS (`U+2BEC`) ... DOWNWARDS TWO-HEADED ARROW WITH TRIANGLE ARROWHEADS (`U+2BEF`).
  - CLOCK FACE ONE OCLOCK (`U+1F550`) ... CLOCK FACE TWELVE-THIRTY (`U+1F567`) (#1850).
* Make below marks to avoid bottom-right Ogoneks (#1789).
* Use oval shape for Empty Set symbols to distinguish with O-Slash (#1822).
* Implement leaning mark mechanism for `F`, `L`, `P`, `b`, `d`, `h`, `k`, `p`, `q`, `r` to get better mark placement. Now, "narrow" marks will align to these letters' extension parts (#1851).
* Add variant selection for Guillemets (#1899).
* Fix detached cedilla in Hookless asymmetric LATIN SMALL LETTER T WITH CEDILLA (`U+0163`) (#1914).
* Fix broken hookless/tailless/asymmetric `t` variants in `ﬅ` ligature (`U+FB05`) (#1915).
* Remove unnecessary tailed variants for Cyrillic Shha with Descender (`U+0527`) (#1916).
* Remove unnecessary lower-right serif variants for Latin Lower K with Descender (`U+2C6A`) (#1917).
* Add italic form of CYRILLIC SMALL LETTER KOMI TJE (`U+050F`) (#1920).
* Remove unnecessary serifed/tailed variants of italic Cyrillic Te with descender (`U+04AD`) and `m` with palatal hook (`U+1D86`) (#1926).
* Remove unnecessary bottom-right serifed variants of Cyrillic Ka with descender (`U+049A`..`U+049B`) (#1927).
* Fix two off-center APL Quad characters in Quasi-proportional (#1930).
* Refine shape of `U+0184`, `U+0185` (#1938).
* Determine serifs of Bulgarian/Serbian De automatically when `g` is double-storey.
* Fix variant assignment of `cv51` for `ss03` under italic slab.
* Fix variant assignment of `cv31`, `cv36`, `cv46`, `cv47`, `cv48`, `cv49`, and `cv51` for `ss18` under italic slab.
