fonttools/Tests/feaLib/data/spec5d2.fea

# OpenType Feature File specification, section 5.d, example 2.
# http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html

# A contiguous set of ligature rules does not need to be ordered in
# any particular way by the font editor; the implementation software
# must do the appropriate sorting.

# So:
feature F1 {
    sub f f by f_f;
    sub f i by f_i;
    sub f f i by f_f_i;
    sub o f f i by o_f_f_i;
} F1;

# will produce an identical representation in the font as:
feature F2 {
    sub o f f i by o_f_f_i;
    sub f f i by f_f_i;
    sub f f by f_f;
    sub f i by f_i;
} F2;