Replacement characters are those black diamonds with a ? in the middle. They are hard to detect. This has info how to do it in a bash script. <https://unix.stackexchange.com/questions/474709/how-to-grep-for-unicode-in-a-bash-script/474812#474812>
Is there a way to do it in Nim? Thanks. The replacement character is used to replace any invalid Unicode character found in the text. It is a "visual aid", not a real character.
