[XeTeX] A Hyphenation Query

[VAFA KHALIGHI]

On page 450 of TeXBook, Donald Knuth says ``The interletter values in these
patterns are all between 0 and 5; a large odd value like 5 forces desirable
hyphen points while a large even value like 4 suppresses undesireable
hyphens''

In the pattern that I want to write, I want to have like 5ZWNJ5 (break
before and after ZWNJ) and I also want to break after non-joinder persian
alphabets so something like ``non-joiner alphabet1'' where non-joiner
alphabet denotes any non-joiner Persian alphabet. I thought this is a
suitable way to do it because if any word contains ZWNJ and a non-joiner
alphabet, then the word will be broken after ZWNJ since ZWNJ has value 5,
but it turned out that my assumption was wrong and the word would break
depending on where of the end of the line it is.

So does this mean that I have toconsider all possible patterns that include
ZWNJ and any non-joiner persian alphabet where I put 5 after ZWNJ and 4
after or before any non-joiner alphabet? or there is an easier approach?

-- 
``Life is not empty,
There is kindness, there is apple and there is faith

One day will come,
and to a mendicant I will endow a jasmine''

-- Sohrab Sepehri
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