fonttools/Lib/fontTools/feaLib/testdata/LigatureCaretByIndex.fea

table GDEF {
    LigatureCaretByIndex [c_t s_t] 11;

    # The OpenType Feature File specification does not define what should
    # happen when there are multiple LigatureCaretByIndex statements for
    # the same glyph. Our behavior matches that of Adobe makeotf v2.0.90.
    # https://github.com/adobe-type-tools/afdko/issues/95
    LigatureCaretByIndex o_f_f_i 66 33;
    LigatureCaretByIndex o_f_f_i 55;
} GDEF;