This property defines the Unicodes which are Tone Mark
Characters like ่,้,๊, etc. are listed under Tone Mark Indic Syllabic Category.
42 Characters are present in Tone Mark Indic Syllabic Category starting with the Unicode point U+0E48 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.