How to Insert NSAttributedString using custom keyboard extension?

Question

I want to write text in some custom fonts using keyboard Extension as these apps (1,2,3,4) are doing. I know how we can insert normal string in document proxy.

Answer 1

The apps you are referring to don't use NSAttributedString or custom fonts. They simply replace letters with similar-looking Unicode characters. You can see these characters in any OS X app inside Edit -> Special Characters menu.