This property defines the Unicodes which are Cluster Break between a base character and a following non spacing mark that takes the form of a vowel
Characters like 각,갂,갃, etc. are listed under Prepend for Vertical Orientation, After Last Grapheme Cluster Break.
10773 Characters are present in Prepend for Vertical Orientation, After Last Grapheme Cluster Break starting with the Unicode point U+AC01 that represents the character 각.
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.