How to handle user input of invalid UTF-8 characters?

Question

I\'m looking for general a strategy/advice on how to handle invalid UTF-8 input from users.

Even though my webapp uses UTF-8, somehow some users enter invalid chara

Answer 1

Set UTF-8 as the character set for all headers output by your PHP code

In every PHP output header, specify UTF-8 as the encoding:

header('Content-Type: text/html; charset=utf-8');