Re: [i18n-activity] Arabic joining across style changes

What is the spec of the zero-width joiner?
1) Unicode-Ch9, Sec 9.2 Arabic, p371 
( says:
"... The use of a joiner **adjacent to a suitable** letter permits 
that letter to form a cursive connection without a **visible 
neighbor**." and gives a use case "This provides a simple way to 
encode some special cases, such as exhibiting a connecting form in 

Guess that "suitable letter" means those letters who join according to
 their writing system (e.g. Aleph doesn't join to it's left in 
But what "adjacent" mean? At the right, left or both?
"without a visible neighbor" : what about no visible member next? A 
visible member but separated by space, say? 
To support the definition, Unicode gives an example of a special case 
with letter HEH and shows what ZWJ means for that special case. 

2) Wikipedia informal définition says: 
 "When placed **between** two characters that **would** otherwise not 
be connected, a ZWJ causes them to be printed in their connected 
More explicit but (only?) "between" two letters. When "would" they be 
not connected.  What are those situations?

Any way, browsers implementation of ZWJ differs from one another. I 
noticed that browsers (based Gecko vs. based Webkit) display depends 
- font used (Amiri seems to react better), 
- What letter is neighbour, even if separated by a space 
- base direction rtl or ltr (!?)

Also, letter Ghain behave differently than letter Heh, though they 
both have four different shapes: initial, medial, final and isolated. 
Moreover, Gecko implementation is right for "colored letters" within a
 word (they join). But ZWJ applied to only one letter works better in 
Webkit implementation : all the four shapes show up .

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Received on Tuesday, 8 November 2016 12:01:58 UTC