If Else Complex button

Hello Geniuses

I’m having some trouble with a movie clip button. Basically I have a button that when you click it it sends you to another frame on the root timeline. This all works fine, however I want the button to stay in it’s transformed state whilst you are in the specific root timeline frame, therefore signifying where you are on the site. Here’s the code I have used -

stop();
this.onEnterFrame = function(){
if(rewind == true){
prevFrame();
}
}

this.onRollOver = function(){
rewind = false;
play();
}

this.onRollOut = function(){
rewind = true;
}

I cannot figure out how to code the next bit. I think I need to use an if/ else statement but am not sure howm I have read loads of posts but cannot translate them to my needs. I have had a guess at something like this (without success -

this.if(_root 19 == true){
_parent.gotoAndStop(4);
}

Any advice would be much appreciated!

Beet