This property defines the Unicodes which are Cluster Break between two characters with a "break opportunity" between them, but it is not a Prepend/Prepend sequence
Characters like ः,ऻ,ा, etc. are listed under Spacing Mark Grapheme Cluster Break.
395 Characters are present in Spacing Mark Grapheme Cluster Break starting with the Unicode point U+0903 that represents the character ः.
Currently, as per latest version 15.0.0, Unicode supports 14 number of Grapheme Cluster Break. Here are a few examples - Base,Carriage Return,Control Neutral, etc.