This is based on: MC-41270
To test this you need the texture pack provided there.
When you type on of these characters like:
in the chat or use it in a tellraw command (/tellraw @p {text:""}) you can see the character like it normally looks: ■ (
Warning: This is NOT the actual character)
But in the book it just looks like a black square (■)
In comparison:
Book
/give @a written_book 1 0 {pages:["{\"text\":\"\",\"extra\":[{\"text\":\"\"}]}"],title:Book,author:TellrawGenerator}
Tellraw
/tellraw @p {text:""}
