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To illustrate, let’s examine a freely available Carolingian minuscule. With liga, it produces results one could use to ease students into a paleography course:

To illustrate, let’s examine a freely available Carolingian minuscule. With liga, it produces results one could use to ease students into a paleography course:

If a font’s liga feature contains many ligatures, it’s easier to keep liga on, break up only the problematic ligatures, and then restore them in rlig. For example, this produces the same output as above:

\documentclass{article}
\usepackage{fontspec}
\directlua{
  fonts.handlers.otf.addfeature{
    name = "nolg",
    type = "multiple",
    data = {
      ['fi'] = { "f", "i" },
      ['fl'] = { "f", "l" },
    },
  }
  fonts.handlers.otf.addfeature{
    name = "rlig",
    type = "ligature",
    data = {
      ['ffi'] = { "f", "f", "i" },
      ['ffl'] = { "f", "f", "l" },
      ['fb'] = { "f", "b" },
      ['ff'] = { "f", "f" },
      ['fh'] = { "f", "h" },
      ['fi'] = { "f", "i" },
      ['fj'] = { "f", "j" },
      ['fk'] = { "f", "k" },
      ['fl'] = { "f", "l" },
    },
  }
  fonts.handlers.otf.addfeature{
    name = "ilig",
    type = "ligature",
    data = {
      ['Th'] = { "T", "h" },
      ['Th.swsh'] = { "T.swsh", "h" },
    },
  }
}
\setmainfont{Newstyle}[
  Script=Default,
  Numbers=OldStyle,
  ItalicFeatures={RawFeature=+ilig},
  RawFeature=+nolg]
\begin{document}
The five baffled officials flew off.

\textit{The five baffled officials flew off.}

\textit{\addfontfeatures{Style=Swash}The five baffled officials flew off.}
\end{document}

In ['f_i'] = { "f", "i" }, ['f_i'] is the glyph name of the ligature, and { "f", "i" } are the letters to be ligatured. So if your font calls the ligature “fi” rather than “f_i”, you should write ['fi'] = { "f", "i" }. Also note that, in some fonts, ['f_f_b'] = { "f", "f", "b" } doesn’t work, but ['f_f_b'] = { "ff", "b" } does.

Crimson isn’t of much use to illustrate removal of ligatures, so here’s FPL Neu (www.alice-dsl.net/ralfstubner/fplneu-otf.html) without its “fk” ligature:

Some fonts put more in their liga feature than one could wish. For example, LTC Kaatskill Pro, a lovely Goudy design, makes œ a standard rather than a discretionary ligature, with the result that not only words like “œdema” but even “does” and “poem” are affected. Using type = "multiple", as for “fk” above, would fix “does” but interfere with “œdema,” so we need another approach.

Besides the harmless “ff,” “fi,” “fl,” “ft,” and “ll,” liga adds an “oe” ligature and e caudata for “ae”; it also replaces “i” and “j” with their dotless versions, and substitutes “ſ” for “s,” “u” for “v,” and “V” for “U.” We can remove those ligatures and substitutions by turning off liga, and add back the harmless ligatures by defining them as rlig, a feature which is on by default:

For example, Goudy’s Newstyle defines “fi” and “fl” in its liga feature, and slightly different “fi” and “fl” glyphs in its dlig feature. There are also glyphs for “ct,” “fb,” “ff,” “ffi,” “fj,” “ffl,” “fk,” “st,” and (in the italic) “Th,” but no feature is defined to ease their use. Adding the two-character ligatures to liga works, but adding the “ffi” and “ffl” ligatures doesn’t, apparently because the “fi” and “fl” ligatures are already in the lookup. But all is well if we turn off liga and define the ligatures we want as rlig:

In ['f_i'] = { "f", "i" }, ['f_i'] is the glyph name of the ligature, and { "f", "i" } are the letters to be ligatured. So if your font calls the ligature ‘fi’ rather than ‘f_i’, you should write ['fi'] = { "f", "i" }. Also note that, in some fonts, ['f_f_b'] = { "f", "f", "b" } doesn’t work, but ['f_f_b'] = { "ff", "b" } does.

Crimson isn’t of much use to illustrate removal of ligatures, so here’s FPL Neu (github.com/rstub/fplneu) without its ‘fk’ ligature:

Some fonts put more in their liga feature than one could wish. For example, LTC Kaatskill Pro, a lovely Goudy design, makes œ a standard rather than a discretionary ligature, with the result that not only words like ‘œdema’ but even ‘does’ and ‘poem’ are affected. Using type = "multiple", as for ‘fk’ above, would fix ‘does’ but interfere with ‘œdema,’ so we need another approach.

Besides the harmless ‘ff,’ ‘fi,’ ‘fl,’ ‘ft,’ and ‘ll,’ liga adds an ‘oe’ ligature and e caudata for ‘ae’; it also replaces ‘i’ and ‘j’ with their dotless versions, and substitutes ‘ſ’ for ‘s,’ ‘u’ for ‘v,’ and ‘V’ for ‘U.’ We can remove those ligatures and substitutions by turning off liga, and add back the harmless ligatures by defining them as rlig, a feature which is on by default:

For example, Goudy’s Newstyle defines ‘fi’ and ‘fl’ in its liga feature, and slightly different ‘fi’ and ‘fl’ glyphs in its dlig feature. There are also glyphs for ‘ct,’ ‘fb,’ ‘ff,’ ‘ffi,’ ‘fj,’ ‘ffl,’ ‘fk,’ ‘st,’ and (in the italic) ‘Th,’ but no feature is defined to ease their use. Adding the two-character ligatures to liga works, but adding the ‘ffi’ and ‘ffl’ ligatures doesn’t, apparently because the ‘fi’ and ‘fl’ ligatures are already in the lookup. But all is well if we turn off liga and define the ligatures we want as rlig: