Readers who choose to look at the following post in the Unicode mailing list archive, then choose to study the pdf document linked from that post may be interested to consider the then following statement in section C of page 5 of that pdf document, listed within the Disadvantages paragraph.
http://www.unicode.org/mail-arch/unicode-ml/y2016-m03/0079.html
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Complex for font designers to implement;
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Could we discuss that please, with particular reference to FontCreator?
William Overington
17 March 2016