How do you detect when to drop a line for a player?

So I made my on custom chat, and to type in it you have to press the Slash key: / which will capture focus of the text box and everything is going well, but when they type a lot of characters it doesn't show since I have clip descendents on so I want to detect when the player reaches the end of one line so it can automatically drop a line in the text box. How do I do that? There is also a multiline option inside the email textbox but I want to be more professional.