This property defines the Unicodes which are Register Shifter
Characters like ៉,៊, etc. are listed under Register Shifter Indic Syllabic Category.
2 Characters are present in Register Shifter Indic Syllabic Category starting with the Unicode point U+17C9 that represents the character ៉.
Currently, as per latest version 15.0.0, Unicode supports 36 number of Indic Syllabic Category. Here are a few examples - Avagraha,Bindu,Brahmi Joining Number, etc.