How do you repeat something on runescape without retyping it?

Answer 1

you press F10 or F11 if u used Quick Chat, but other players may use an auto-typer which is illegal and you will get banned for using one

Answer 2

There is no such option. If you see anybody typing the same text over and over again, they are probably using an external program. This is against the rules, and will get you banned.