Changing font when certain character is used

I’m trying to create a sudo-syntax script so when I user types particular characters the font color(or size)changes. For example, in the text box if they typed a { in the following:
The sky is [COLOR=”Red”]{cloudy and dark}[/COLOR] but it is still warm.

or

The sky is [SIZE=”5″]{cloudy and [SIZE=”6″]{dark}[/SIZE]}[/SIZE] but it is still warm. (recursive)

So every time { is used it changes the font, and when } is used it moves it back to the previously used font.

Strange examples I know, but if I can figure this out I can continue on. I will also be using php with it. This has to work when they user either types it into the text box, or pastes it. Anyone familiar or have ideas for this?

Thanks!

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