Specials (Unicode block)

[5] The replacement character � (often displayed as a black rhombus with a white question mark) is a symbol found in the Unicode standard at code point U+FFFD in the Specials table.

It is used to indicate problems when a system is unable to render a stream of data to correct symbols.

A design that is better (but harder to implement) is to preserve the original bytes, including any errors, and only convert to the replacement when displaying the text.

This will allow the text editor to save the original byte sequence, while still showing an error indication to the user.

The following Unicode-related documents record the purpose and process of defining specific characters in the Specials block: