fonttools/Tests/feaLib/data/spec5d1.fea

# OpenType Feature File specification, section 5.d, example 1.
# http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html

feature F1 {
  sub [one one.oldstyle] [slash fraction] [two two.oldstyle] by onehalf;
} F1;

# Since the OpenType specification does not allow ligature substitutions
# to be specified on target sequences that contain glyph classes, the
# implementation software will enumerate all specific glyph sequences
# if glyph classes are detected in <glyph sequence>.  Thus, the above
# example produces an identical representation in the font as if all
# the sequences were manually enumerated by the font editor:
#
# NOTE(anthrotype): The previous sentence is no longer entirely true, since we
# now preserve the order in which the ligatures (with same length and first glyph)
# were specified in the feature file and do not sort them alphabetically
# by the ligature component names. Therefore, the way this particular example from
# the FEA spec is written will produce two slightly different representations
# in the font in which the ligatures are enumerated differently, however the two
# lookups are functionally equivalent.
# See: https://github.com/fonttools/fonttools/issues/3428
# https://github.com/adobe-type-tools/afdko/issues/1727
feature F2 {
  sub one slash two by onehalf;
  sub one.oldstyle slash two by onehalf;
  sub one fraction two by onehalf;
  sub one.oldstyle fraction two by onehalf;
  sub one slash two.oldstyle by onehalf;
  sub one.oldstyle slash two.oldstyle by onehalf;
  sub one fraction two.oldstyle by onehalf;
  sub one.oldstyle fraction two.oldstyle by onehalf;
} F2;