Is Multiple Substitution decomposing a lig. glyph?, when and why you have to do it

WAY KYI

To me, Multiple Substitution feature is doing decomposition of a lig. glyph and 
not sure why you have to do it. I do not grasp the concept of it.
Why in the first place you do a lig. glyph with two or more glyphs and then decompose them
back to two/more glyphs later. I knew there must be a valid reason why you do it, so what is the reason?
Can you kindly show me the example codes and the reason, when it needs this feature?
Thanks

Simon Cozens

It doesn't need to decompose a ligature - it just substitutes one glyph with more than one glyph. See some examples here: https://simoncozens.github.io/fonts-and-layout/features-2.html#multiple-substitution

WAY KYI

Thank you very much again. There are so much information beginner like me need to learn. Thanks