This property defines the Unicodes which belongs to Cyrillic Extended B block
Characters like Ꙁ,ꙁ,Ꙃ, etc. are listed under Cyrillic Extended B Block.
96 Characters are present in Cyrillic Extended B Block starting with the Unicode point U+A640 that represents the character Ꙁ.
Currently, as per latest version 15.0.0, Unicode supports 328 number of Block. Here are a few examples - Latin Extended E,Adlam,Aegean Numbers, etc.