Short anecdote: A few years ago I had to fill in some translation keys within a ecommerce shop gui. Eventually, I had to revert some key to it's default value

Short anecdote: A few years ago I had to fill in some translation keys within a ecommerce shop gui. Eventually, I had to revert some key to it's default value and therefore tried to copy and paste the displayed default value, but the system always refused to take that value. It complained that the string contained invalid characters, but I wondered because I just inserted the previous valid default value and to my eye there where not special characters anyway?!? So I called one of the devs and after a few minutes he told me, that the output I copied contained a zero-width space and that character was not allowed by the validation engine. So when I typed the string myself everything went fine ;-) Nowadays, I like to consult `hexdump -C` in such cases.