fonttools/Tests/feaLib/data/spec6b_ii.fea

# OpenType Feature File specification, section 6.b.ii:
# [GPOS LookupType 2] Enumerating pairs
# http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html

@Y_LC = [y yacute ydieresis];
@SMALL_PUNC = [comma semicolon period];

feature kern {
  enum pos @Y_LC semicolon -80;    # specific pairs
  pos f quoteright 30;         # specific pair
  pos @Y_LC @SMALL_PUNC -100;  # class pair
} kern;