This property defines the Unicodes which are of Dual Joining Type
Characters like ؠ,ئ,ب, etc. are listed under Dual Joining Joining Type.
610 Characters are present in Dual Joining Joining Type starting with the Unicode point U+0620 that represents the character ؠ.
Currently, as per latest version 15.0.0, Unicode supports 6 number of Joining Type. Here are a few examples - Dual Joining,Join Causing,Left Joining, etc.