I stumbled upon an interesting character while skyping. I was initially interested to send an empty message but, since Skype has some validation rules, it doesn't allow empty messages.
But, with a few ALT+NUMPAD ASCII symbols I saw that for alt+777 it returns ○ on most editors and ̉ on skype, which delivers an empty-like message and this is where curiosity got to me. I started to abuse this symbol and noticed that it can overlap other characters. So if I write the ASCII symbol on a word, the result would be a ̉mủt̉ả̉̉̉t̉ẻd̉W̉ỏ̉r̉̉d̉̉.
You can see for yourself that "̉mủt̉ả̉̉̉t̉ẻd̉W̉ỏ̉r̉̉d̉̉".length == 24 while "mutatedWord".length == 11.
And the funny thing is that, up until now, I could only generate that weird aphostrophy on skype, anywhere else it results in ○.
Can someone explain this behavior to me?
You're writing Unicode codepoint 777 (but usually notated in hex as U+0307). This codepoint is one of Unicode's combinbing characters, namely "combining hook above". You've already discovered what they do: they add a diacritic to the next character.
If there's no letter following, there's no consisitent behavior. If Skype renders it differently from the other apps you've tried, it probably is using a different font engine.