How do you make a text editor?

How do you make a text editor? I know it's hard . . . because I've looked inside some of them. Some of them has complicated code. Is there anyone good with text editors that can help me?

Another question: Does it work if I do this?

You create a sprite that contains all the letters, symbols etc, you want in your text editor, then when a certain key pressed, switch to that sprite and create clone and change x by 20 or something. For example, if the key a is pressed, then the sprite will create a clone with the costume a and move 20 steps.

Thanks!