This property defines the Unicodes which belongs to Katakana Phonetic Extensions block
Characters like ㇰ,ㇱ,ㇲ, etc. are listed under Katakana Phonetic Extensions Block.
16 Characters are present in Katakana Phonetic Extensions Block starting with the Unicode point U+31F0 that represents the character ㇰ.
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.